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Stars and Telescopes 



Concerning the Sun, wrote Sir William Herschel 
in the opening year of the 19th century, e The influ- 
ence of this eminent body on the globe we inhabit is so 
great and so widely diffused that it becomes almost a 
duty to study the operations which are ca7~ried on upon 
the solar surface? 



Pulrijra • sunt • ntimfa • f actente • 2Te • tt ■ rcce • 2Eu 
inmarrabilito • pulrijrior • qui • fcctsti • omnia ■ 

— s. aurelii AUGUSTINI Confessiones 



Stars and Telescopes 

A Hand-book of Popular Astronomy 



Founded on the 9th Edition of 
Lynn's Celestial Motions 



BY 

DAVID P. TODD 

M.A., PH.D. 

Professor of Astronomy and Director of the Observatory , Amherst 
College. Author of "A New Astronomy," etc., etc. 




BOSTON 
LITTLE, BROWN, AND COMPANY 
1899 
L. 



29403 



Copyright, 1899, 
By Little, Brown, and Company 



All rights reserved. 



TW0 00P|fe^„ 6BS|vlB 







John Wilson and Son, Cambridge, U.S.A. 






DEDICATED 



TO 



M rs D. WILLIS JAMES 



PREFACE 



<?TARS AND TELESCOPES is intended 
to meet an American demand for a plain, 
tinrhetorical statement of the astronomy of to- 
day ; and it has been based upon M r Lynn's 
Celestial Motions, because his little book had 
already covered excel- 
lently part of the ground, 
and had passed through 



nine English editions. 




Permission for this use of 
Celestial Motions was 
most courteously granted 
by its author, formerly 
of the Royal Observa- 
tory at Greenwich. In 
accord with M r Lynn's 
wish, I have indicated 
which is his work and which my own, both in 
situ, and on the page of contents. For the 
greater part of Chapter XVI I am indebted to 
the kindness of D r See. 

With a single exception, the ample illustra- 
tions are wholly new additions. For excellent 



WILLIAM THYNNE LYNN 



vi Preface 

photographs I acknowledge gratefully my in- 
debtedness — 

To M rs Henry Draper of New York, 

To MM. Loewy, Deslandres, and Henry of Paris, 

To M r Christie, Astronomer Royal of Greenwich, 

To D r Gill, H. M. Astronomer at the Cape, 

To Sir Howard Grubb of Dublin, 

To D r Roberts of Crowborough Hill, Sussex, 

To Professor Young of Princeton University, 

To Professor Langley, Secretary of the Smithsonian 

Institution, 
To Professor Rowland of the Johns Hopkins University, 
To Professor Pickering, Director of Harvard College 

Observatory, 
To Commodore Phythian, U. S. Naval Observatory, 
To Professor Hale, Director of the Yerkes Observatory, 
To M r Brashear, Director Allegheny Observatory, 
To Messrs Warner and Swasey of Cleveland. 

For the use of illustrations in astronomical 
periodicals also — 

To the Editors of the Vierteljahrsschrift der Astro- 

nomischen Gesellschaft (Leipzig), 
To the Editors of Bulletin Astronomique (Paris), 
To the Editor of Nature (London), 
To the Editors of The Observatory (London), 
To M. Flammarion, Editor of L' Astronomie, 
To D r Schwahn, Editor of Himmel tend Erde (Berlin), 
To M r Maunder, Editor of Knowledge (London), 
To D r Chandler, Editor of The Astronomical Journal, 
To Professor Payne, Editor of Popular Astronomy, 
To Professor Hale, Editor The Astrophysical JournaL 



Pre fa: vii 

For the courteous loan of engraved blocks 
also — 

To D r Barnard of the Yerkes Observatory, 

To Professor Payne, Director North field Observatory, 

To the American Book Company of New York, 

To the Messrs D. Appleton & Company of New 

York, 
To the G. & C. MERRIAM Company of Springfield. 

For the use of illustrations in printed volumes 
likewise — 

To MM. Gauthier Villars et Fils of Paris (Father 

Secchi's Le Soldi, and M. Flammarion's La Plane te 

Mars), 
To W. Exgelmaxx's Verlag of Leipzig (D r Vogel's 

Populare Astronomie, and D r Schelxer's Die Pho- 
tographic der Gestime), 
To Hartlebex's Verlag of Vienna (Baron v. Schweiger- 

Lerchexfeld's Atlas der Himmelskunde) , 
To Messrs A. and C. Black of Edinburgh (D r 

Dreyer's Tycho Brake). 
To Messrs Taylor and Fraxcis of London (M r Den- 

xixg's Telescopic Work for Starlight Evenings) , 
To Edward Stanford of London (M r McClean's 

Photographic Spectra of the Sun and Metals), 
To Messrs Houghton, Mifflin & Company of Boston 

(M r Lowell's Annals, vol. i., and M rs Todd's Corona 

and Coro7iet), 
To Messrs Longmans, Green & Company of New 

York (M r Proctor's Old and New Astronomy), 
To Messrs Charles Scribner's Sons of New York 

(Scribner's Magazine) . 

Many of the portraits of astronomers are taken 
from the published volumes of their lives and 



viii Preface 

works, to the editors and publishers of which 
due acknowledgment is here returned. To the 
courtesy of M rs ADAMS I am indebted for the ap- 
propriate design of Adams's Ex Libris. Other 
portraits have been made available through the 
kindness of relatives and executors. 

Stars and Telescopes has advantaged greatly 
from the criticism of several astronomers who 
have examined chapters in proofs, though no 
one will hold them responsible for any errors 
that may have escaped notice : — 

The late Professor Newton of Yale University, Me- 
teors and Meteoric Bodies, 
M. Charlois of Nice, The Small Planets, 
Professor Newcomb of Washington, The Planets, 
Professor Young of Princeton, The Sun, 
Professor Pickering of Cambridge, The Fixed Stars,. 
M r Lowell of Boston, The Ruddy Planet, 
Professor Barnard of Williams Bay, The Comets. 

To all I am glad to accord my obligation in 
fullest measure. 

DAVID P. TODD. 
Observatory House, 

Amherst: March 1899. 

*^* While this work is passing through the press, announce- 
ment is made of an important discovery by Professor W. H. 
Pickering at the Harvard Observatory, of a ninth moon of 
Saturn (page 129), with a period of about 2\ years, and five 
times more distant from Saturn than Japetus, the outermost 
satellite hitherto known. The new moon has been named 
Phoebe, and it is probably about 200 miles in diameter. — 
2C//& March 1899. 



CONTENTS 



Chapter Page 

Introduction ( Todd) i 

I. Outline of Astronomical Discovery [Lynn) 9 

II. The Earth {Lynn and Todd) 19 

III. The Moon [Lynn and Todd) 26 

IV. The Calendar (Lynn and Todd) .... 34 
V. The Astronomical Relations of Light 

(Lynn and Todd) 41 

VI. The Sun (Lynn and Todd) 48 

VII. More about the Sun — Solar Physics 

(Todd) 69 

VIII. Total Solar Eclipses (Todd) 82 

IX. The Solar System (Lynn and Todd) ... 90 

X. The Planets (Lynn and Todd) . . . . . 104 

XI. The Ruddy Planet (7 odd) 155. 

XII. Comets (Lynn and Todd) 181 

XIII. Meteoric Bodies (Lynn and Todd) .... 208 

XIV. Meteoric Bodies — continued (Todd) . . . 220 
XV. The Constellations (Lynn and Todd) . . 231 

XVI. The Cosmogony (See) 242 

XVII. The Fixed Stars (Lynn and Todd) . . . 255 

XVIII. Telescopes and Houses for them (Todd) 316 



Table of the Small Planets (Todd) . . 397 
Index (Todd) 409 



LIST OF ILLUSTRATIONS 



Page 
Seasonal changes on Mars (Lowell) . . . frontispiece in eo/ors 

Portrait of William Thynne Lynn v 

Portrait of Nicholas Copernicus n 

Portrait of Galileo Galilei 12 

Hersch el's 40-foot reflector 13 

Portrait of Sir William Herschel 14 

Portrait of Joseph von Fraunhofer 17 

Portrait of Jean Sylvain Bailly opposite 18 

Portrait of Jean Joseph Delambre opposite 18 

Position of the vernal equinox, b. c. 2170 22 

Present position of the vernal equinox 22 

Land hemisphere of the Earth 24 

Water hemisphere of the Earth 24 

Trajectory of the Earth's north pole (Chandler) . . opposite 24 

Portrait of Peter Andreas Hansen opposite 26 

Portrait of Charles Eugene Delau nay ... . opposite 26 

A part of the Moon (photographed by Henry) . . . opposite 28 

Surface of the Moon (photographed at the Lick Observatory) . 29 

Jupiter in occultation (Denning) 30 

The Moon (photographed by Loewy and Puiseux) . opposite 30 

The Royal Observatory at Greenwich 39 

The photo-tachometer (Newcomb) 44 

Portrait of Olaus Roemer 45 

Portrait of James Bradley 46 

Portrait of Jean Bernard L£on Foucault 47 

Relative distance and size of Sun, Earth, and Moon .... 49 

Portrait of Edmund Halley 50 

A group of sunspots (Rutherfurd) 52 

The Sun (photographed by Ruth erfurd) 57 

Sunspot highly magnified (Secchi) 58 

Sunspot zones according to Proctor 59 

12-inch equatorial at Potsdam, Germany 60 

The Potsdam Astrophysical Observatory 61 

The Sun's surface (photographed by Janssen) 62 



xii List of Illustrations 

Page 

Great protuberance of 1886 63 

Eruptive protuberance (Trouvelot) 63. 

1 Great Horn ' of the eclipse of 1868 . . - 63 

Sunspots and zones of faculae (Hale) 64. 

Zones of solar faculae (Deslandres) opposite 64. 

Solar chromosphere (Deslandres) opposite 64 

Great sunspot of September 1898 i opposite 64 

The Sun's chromosphere (Hale) 65 

Latitude of spots and protuberances 66> 

Spots and magnetic declination (Wolfer) 67 

Portrait of Gustave Robert Kirchhoff 71 

Ruling engine (Rowland) 72 

Spectra of the Sun and metals (McClean) .... opposite 72 

Bolometer in water jacket (Langley) y2~ 

Portrait of Hermann Ludwig Ferdinand von Helmholtz yy 

Diagrams of Eclipses (Ball) 8$. 

Corona of 1882 (Wesley and Schuster) 86 

Portrait of Theodor von Oppolzer opposite 86 

Portrait of Stephen Joseph Perry opposite 86- 

Corona of 1878 (Harkness) 87 

Tracks of future eclipses (Todd) opposite 88 

Corona of 1898 (Maunder) 89. 

Portrait of Tycho Brahe 91 

Portrait of Johann Kepler 92 

Kepler's second law 93, 

Portrait of Sir Isaac Newton 93. 

Relative size of Sun, planets and satellites 95 

Portrait of Leonhard Euler 96 

Portrait of Joseph Louis La Grange 97 

Portrait of Karl Friedrich Gauss 99. 

The U. S. Naval Observatory, Washington 101 

Portrait of Sir George Biddell Airy 102 

Portrait of Pierre Gassendi 104. 

Mercury (after Schiaparelli) 105 

Venus (Niesten and Stuyvaert) 107 

Venus near inferior conjunction (Barnard) 108 

Venus (after Trouvelot) 108' 

Mercury (after Lowell) opposite 108 

Venus (after Lowell) opposite 10S 

Mars (after Flammarion) in 

Orbits of satellites of Mars 112 

Portrait of Christian Henry Frederick Peters .... 113 

Jupiter (after Keeler) 118'. 

The Lick Observatory 122: 

Jupiter (after Knobel) 123 



L 1st of Illustrations x i i i 

Pagb 

Jupiter's satellite in (Campbbll and Schabberle) .... 124 

Eye-end of the Lick telescope 124 

The Lick 36-inch telescope 125 

Saturn and his rings 127 

The Imperial Observatory at Pulkowa 130 

Portrait of Jean Dominique Cassini opposite 132 

The Pulkowa 30-inch telescope 133 

Portrait of Benjamin Peircb 136 

Uranus (after Henry) 138 

The Paris Observatory 141 

Portrait of URBAIN Jean JOSEPH Le Verrier T42 

Portrait of John Couch Adams .143 

Portrait of Felix Francois Tisserand 146 

Portrait of Mary Somerville 150 

Portrait of James Craig Watson 152 

Portrait of Heinrich YVilhelm Matthias Olbers . . . 153, 

Birthplace of Newton 154 

Portrait of Dominique Francois Arago 155 

Portrait of Friedrich Kaiser 157 

North polar cap of Mars (Knobel) 160- 

Dwindling of south polar cap (Lowell) opposite 162 

Mars (after Perrotin) 164 

Detail of Martian canals 165 

Solis Lacus region (Douglass) 166 

Mars (after Brenner) 167 

The Observatory at Nice (Bischoffsheim) 169' 

Mars (after Cerulli) 171 

Mars (after Pickering) 172 

Mars in 12 presentations (Lowell) opposite 176 

Halley's Comet (after Struve) 182 

The Great Comet of 1861 (Williams) 183 

Head of Great Comet of 1861 (Secchi) 183 

Brooks's Comet (1886 v) 184 

Pons-Brooks Comet (1883) iSS 

Pons-Brooks Comet (after Swift) 188 

Portrait of Caroline Herschel 189- 

Portrait of Johann Franz Encke 190 

Biela's double comet 192 

Swift's Comet (Barnard) 194 

The Great Comet of 1843 199 

Gale's Comet (photographed by Barnard) .... opposite 200 

Don ati's Comet (Bond) 203 

Portrait of Maria Mitchell 204 

The head of Coggia's Comet (Brodie) 205 

Portrait of Ernst Florens Friedrich Chladni .... 208- 



xiv List of Illustrations 

Page 

Portrait of Dexison Olmsted 210 

Apparent radiation of meteors (Denning) 211 

Photographing meteor-trails (Elkin) . 212 

Portrait of Friedrich August Theodor Wixxecke opposite 212 

Portrait of Hubert Anson Newton opposite 212 

Path of the November meteors 213 

Telescopic meteors (Brooks) 214 

Meteor of iSSS (Denning) 214 

Path of August meteors in space 215 

Brooks Comet of 1890 (Barnard) 218 

The Paris collection of meteorites 221 

Meteoric iron from South Africa 223 

Widmannstatian figures 225 

Pseudo-meteoric iron of Ovifak 226 

The Pleiades (naked-eye view) 236 

The Pleiades (photographed by Henry) 237 

The great nebula in Orion (Roberts) 238 

Portrait of William Cranch Bond 240 

The great nebula in Andromeda (Roberts) 243 

Portrait of Immanuel Kant 245 

Portrait of Pierre Simon La Place 246 

Lord Rosse's 6-foot reflector 247 

Portrait of Lord Rosse 248 

Orbit of Alpha Centauri (See) 250 

Double nebula in Virgo 251 

The figure of Poincar£ 252 

Portrait of Eduard Heis 256 

The Milky Way in Sagittarius (Barnard) 257 

The meridian photometer (Pickering) 258 

Photographic equatorial telescope (Grubb) 259 

Portrait of Friedrich Wilhelm August Argelander . . 261 

Portrait of Benjamin Apthorp Gould 262 

The Bruce 24-inch telescope 264 

Vicinity of Eta Carinae (Bailey) 265 

Cluster Omega Centauri (Herschel) 269 

Portrait of Eduard Schonfeld 270 

Portrait of Friedrich Wilhelm Bessel 273 

Portrait of Christian August Friedrich Peters . . . 274 

Portrait of Franz Friedrich Ernst Brunnow .... 275 

Portrait of Hugo Gylden 276 

Heliometer at Capetown (Gill) 277 

Divided object-glass of heliometer 279 

Distances of stars trom the Sun 2S0 

Typical double star systems 281 

Portrait of Friedrich Georg Wilhelm Struve .... 282 



List of Illustrations 



XV 



Page 

trait of William Rutter Dawes 283 

Orbit of Gamma Virginis 284 

Orbit of the Companion of Sinus 284 

Portrait of Alvan Graham Clark 285 

Portrait of Johann Christian Dopplbr 286 

spectroscope by Brashear 288 

Observatory of D r Isaac Roberts, F. R. S 290 

20-inch reflector (Grubb j 292 

Globular cluster in Pegasus (Roberts) 293 

trurn oi Sirius and iron (Vogel) 294 

Portrait of Pietro Angelo Secchi 294 

Types of stellar spectra (Secchi) 296 

Cluster in Perseus (Roberts) 297 

Portrait of HENRY Draper 298 

The Bache telescope at Cambridge 299 

Harvard College Observatory 300 

Spectrum of Capella (Deslandres) 301 

Portrait of Sir John Herschel 302 

Distribution of nebulae and clusters (Waters) 304 

Portrait of Richard Anthony Proctor 305 

Portrait of Johann von Lamont 308 

Ring nebula in Lyra (Roberts) 309 

Spiral nebula in Canes Venatici (Roberts) 310 

Portrait of Christian Huygens 317 

17th century telescope (Hevelius) 318 

A modern field-glass (Bausch and Lomi ) 319 

A modern reflector (Brashear) 321 

The Melbourne 4-ft. reflector (Grubb) 322 

Portrait of Thomas Grubb 323 

Portrait of Arthur Cowper Ranyard 326 

Course of rays through telescope .... 327 

Portrait of John Dollond 328 

Portrait of David Rittenhouse 329 

Portrait of Ormsby MacKnight Mitchel 330 

Triple object-glass (Taylor) 331 

Vienna 27-inch equatorial (Grubb) 333 

The Imperial Observatory at Vienna 334 

Portrait of Alvan Clark 335 

Portrait of George Bassett Clark 336 

Yerkes Observatory of University of Chicago 2>37 

40-inch telescope of the Yerkes Observatory 33S 

Equatorial Coude (Loewy) 3-1 o 

Micrometer (schematic) 342 

A modern micrometer 343 

Portrait of Lewis Morris Rutherfurd 344 



xvi List of Illustrations 

Page 

40-foot horizontal photo-heliograph 345 

Plate-measuring engine (Repsold) 348 

Variable nebula surrounding Eta Carinae 350 

Spectro-heliograph (Brashear) 3-2 

Universal spectroscope (Brashear) y^ 

Discovery of a small planet by photography (Wolf) . ... 35 c 

Modern camera for stellar photography (Heyde) ^-7 

Meteor-trail (photographed by Barnard) 3-9 

The pneumatic commutator (Todd) 361 

-Automatic photography of the Corona (Todd) 362 

The electric commutator (Todd) ^6^ 

Flash-spectrum, eclipse of 1898 (Naegamvela) 364 

Hevelius and his consort observing 365 

The Repsold meridian circle of Carleton College 368 

..Automatic dividing-engine (Secretan) 369 

Portrait of Franz Xaver von Zach 370 

The Almucantar (Chandler) 3^ r 

Portrait of John Harrison , 372 

Portrait of Johann Tobias Mayer ^73 

Portrait of Nathaniel Bowditch 374 

Smith College Observatory 375 

Oxford University Observatory 376 

Manora Observatory, Istria ^77 

3-inch portable telescope ^77 

Portrait of Thomas William Webb 27S 

Portrait of James Lick 380 

Portrait of Uriah Atherton Boyden 381 

The Boyden Observatory, Arequipa, Peru 3S2 

Portrait of Elias Loomis 383 

.Portrait of John Couch Adams (ex libris) 385 



INTRODUCTION 



A STRONOMY may be styled a very aristocrat 
among the sciences ; but, while its cosmic 
conceptions never fail to arouse the broadest 
general interest, it is an interest that has by no 
means led to a knowledge of this engrossing 
science proportionately widespread. 

Antecedent to the 19th century, astronomy 
was purely a science of celestial motions'. Its 
mystical parent, astrology, had taught that 
planetary places influence men's destinies : how 
important then, to know the place of every 
planet in the past, and to be able to divine their 
conjunctions in the future. Astrology was utili- 
tarian to this end, and her offspring was hardly 
less so ; for upon a knowledge of celestial mo- 
tions, still farther refined and perfected, were 
founded the indispensable and very practical 
arts of conducting merchant ships from port to 
port in safety, and of surveying accurately coast 
lines and other national boundaries. 

But with the beginning of the 19th century 
came the brilliant and imaginative conceptions 
of the elder HERSCHEL, concerning the consti- 
tution and physical peculiarities of the heavenly 



2 Introduction 

bodies, based upon his minute and painstaking 
scrutiny ; for his thought was acute, as his ob- 
servation was thorough. Still it did not so 
much concern him where these bodies were as 
what they were. Sir WILLIAM HERSCHEL, in- 
deed, was the first to build monster telescopes of 
modern excellence, and he vastly augmented 
our knowledge of the heavens by faithfully using 
them. Also he prepared the foundation upon 
which the imposing edifice of physical astronomy 
has been erected by his followers. 

As the marvellous revelations of the heavens 
have come to us mainly through the telescope 
in the hands of highly skilful astronomers, men- 
tion of their labors is associated with the tele- 
scopes that made the researches possible. In- 
evitably these are intimately related : we cannot 
neglect the human element, though we may affect 
to do so. Thereby may human interest lead to 
wider diffusion of astronomical knowledge. 

So the book is embellished also by a profusion 
of portraits of astronomers, among those not liv- 
ing, — of many whose important work was done 
so unostentatiously that their names have long 
since passed from merely popular recognition. 
Noteworthy and impersonal achievement is 
everywhere associated with the distinguished 
lives that have passed in unselfish discovery of 
astronomical truth — lives of unswerving devo- 
tion, of persistent self-sacrifice, of unwearying 
toil, and here and there of sad disappointment, 
and even pathetic disaster. 



Introduction 3 

Next in our abiding concern with astrono- 
mers and their labors are the tools with which 
their work is accomplished — telescopes not 
only, but all those modern adjuncts introduced 
by the physicist, and called photometers, spec- 
troscopes, and bolometers, as well as the multi- 
fold adaptations of the photographic camera 
which have revolutionized nearly all departments 
of the science, and afforded a welcome and 
unquestioned service. Nor have I neglected 
either the men who made the telescopes or the 
buildings in which all such instruments are 
housed. 

Stars and Telescopes begins with a running 
commentary or outline of astronomical discov- 
ery, with a rigid exclusion of all detail. Second 
and third chapters deal almost as briefly with 
the Earth, and the Moon, our nearest celestial 
neighbor in good and regular standing. Due 
prominence is given that occult phenomenon of 
recent discovery, called technically the variation 
of latitude; so persistently has research upon it 
been prosecuted that the tiny oscillations of the 
Earth's axis within the globe itself can be pre- 
dicted for a decade to come. So signally has 
photography aided in delineation of the surface 
of our satellite that photographs, reproduced by 
the best modern processes, have been made to 
serve instead of word descriptions of lunar 
scenery. Of less popular interest is the Calen- 
dar. But a chapter on the astronomical relations 
of light is intended to emphasize the prime sig- 



4 Introduction 

nificance of this phenomenon in all celestial 
enquiry. Without it the heavens would be as a 
book forever sealed. 

The Sun, monarch of the. planetary system, 
and source of all our light and life, could not 
be dismissed without the fuller treatment de- 
manded by his importance. The ever new 
problem of his distance from us, providing 
as it does our foot-rule of the universe; the 
continually changing appearances of his sur- 
face; the power of his light, and the intensity 
and maintenance of his heat — all are set forth, 
not only the most recent results, but the instru- 
ments and methods by which in part they have 
been derived. 

Solar eclipses, too, are introduced, but only 
in the most general fashion. Their prediction is, 
however, exciting sufficiently wide interest to 
warrant a table and chart of these engrossing 
phenomena in the future. 

The chapter embodying a general outline of 
the solar system necessarily brings to the read- 
er's attention the labors of the most celebrated 
of all the early astronomers — TYCHO, KEPLER, 
and NEWTON. But an account of the individual 
planets of our system called for still farther ex- 
pansion, if the present state of our knowledge of 
those bodies was to be abundantly set forth. 
Particularly have the most recent results been 
presented, with a view of exhibiting in a popular 
way the state of technical literature down to the 
present day. Wherever the desired verification 



Introduction 5 

•of theory or observation is still lacking, T have 
been careful to say so. 

In the summer of 1898 was discovered a new 
planet, probably a genuine member of the aster- 
oidal group, although periodically it approaches 
nearer to the Earth by one-half than Venus ever 
does, thereby outclassing not only this planet 
when in transit over the Sun's disk, but Mars 
also at his close oppositions, as a medium for 
finding the Sun's true distance from us. Fresh 
interest attaching to the small planet group as 
a whole, I have appended in tabular form a 
complete list of these tiny members of the solar 
system, but without amplifying it to include 
particularities of their paths round the Sun. 

The chapter on Comets deals especially with 
historic detail of these filmy voyagers ; and the 
great meteoric showers of 1899 and 1900 must 
be justification for extending the space allotted 
to meteorites — the sole material messengers 
from outer space ever known to come within 
human reach. 

Even more amplified is the chapter on the 
fixed stars and nebulae, because the methods of 
the new astronomy have achieved unparalleled 
revelations in the stellar realm. So fertile are 
the starry fields, and so persistently have they 
been tilled by a band of tireless workers for the 
last quarter of a century, that the compacting of 
results into a single chapter was found impos- 
sible. The cosmogony was therefore allotted a 
•chapter by itself, and due space accorded the 



6 Introduction 

newest research in our knowledge of the building 
and development of worlds. 

Both to encourage and to gratify a desire to 
consult original sources, there is added to each 
chapter a bibliographic note, never intended to 
be complete, and with both popular and scientific 
papers purposely intermingled. 

But nearly equal in interest with the stars 
themselves are the telescopes by which alone we 
ascertain their distances, inconceivably vast, and 
the spectroscopes that tell the tale of stellar 
motion and constitution. So Stars and Telescopes 
may be said to culminate in an account of the 
famous instruments, their construction and mount- 
ing and use. To the gradual development of 
skill in the arts and to present-day perfection 
of mechanical and photographic methods is the 
progress of astronomy vastly indebted in all its 
ramifications. Just as the precision of the ' old 
astronomy' could never have been attained in- 
dependently of the skill of workers in metals 
who provided accurate clocks and meridian 
circles, so the ' new astronomy ' would have 
been wholly handicapped in its development 
but for the splendid prisms and perfect gratings 
of the modern optician. Evolution, too, of the 
process of making great lumps of glass has been 
mainly mechanical, not to mention the methods 
of fashioning disks into lens and prism. During 
the first half of the 19th century, there was little 
chance to forget the optician and telescope 
builder, because the greatest instruments of 



Introduction 7 

those days were constructed by the astronomers 
themselves, who used them so successfully. 
Too often, however, in our own day we omit to 
mention the optician and instrument maker, 
unaided by whose consummate skill original 
research in physics and astronomy would have 
made but slender progress. Not only in the 
title of this book, therefore, are the significant 
labors of the mechanician recognized, but its 
last chapter is lengthened to a degree fitting a 
highly mechanical age. 

By the most conservative estimate, the thresh- 
old of the edifice of stellar investigation is but 
barely crossed ; its corridors have been sub- 
jected to the merest reconnaissance; nothing 
but the crudest plan of the intricate temple of 
the stars can yet be sketched with confidence. 
Here comes an insistent demand for more light 
and greater telescopes still — more light, not for 
the expected discovery of new bodies, but for 
studying in greater detail the constitution of the 
component bodies of the stellar universe already 
known, and for investigating with greater pre- 
cision their motions relatively to our solar orb 
and his tributary family of planetary globes. 

Greater successes for the optician of the future 
seem safely predicated upon the rapid advances 
of the recent past. No step can, however, be 
taken except at infinite pains and large expen- 
diture. Mechanician and optician are ready to 
do their faithful part, and opportunity to go 
forward must not be too long denied them. 



8 Introduction 

Continuity of effort will alone guarantee success ; 
each generation must build upon the platform of 
its immediate predecessor. Otherwise gaps oc- 
cur. With the passing of the elder HERSCHEL, 
nearly a generation elapsed before Lord Rosse's 
great telescope was finished ; and he could then 
profit relatively but little by HERSCHEL's un- 
paralleled experience. Already the Clarks 
have passed from earth, father and both sons. 
But we have worthy successors, still in the prime 
of brilliant achievement : they await to-day their 
keenly coveted opportunity. 

D. P. 71 

Amherst, February 1899. 



STARS AND TELESCOPES 



CHAPTER I 

OUTLINE HISTORY OF ASTRONOMICAL 
DISCOVERY 

T T is not proposed here to enter into any discussion 
-■- of the knowledge of astronomy possessed by the 
ancient Egyptians, Babylonians, or other Eastern na- 
tions. Among the Greeks, Eudoxus, born at Cnidus 
in Caria about b. c. 409, is the first astronomer that 
need be named. His works have not come down to 
us ; but it is known that one of them was a description 
of the constellations, which is versified in the Phai- 
?iome?ia of Aratus of Soli in Cilicia, and is the work 
quoted by Paul in his speech before the Areopagus 
at Athens. 

The greatest of the ancient Greek astronomers was 
Hipparchus, who, though a native of Nicsea in Bithy- 
nia, made most of his observations at Rhodes. He 
was the first to form a systematic catalogue of stars, 
induced to do so by the appearance of a new star in 
the heavens, which is thought to be the same as one 
recorded in the Chinese annals as having appeared in 
the constellation Scorpio in the year corresponding to 
b. c. 134. The most probable date of the death of 
Hipparchus is b. c. 120. His catalogue is known to 



Io Stars and Telescopes 

us only by its incorporation, with some modifications, 
into the great work of the Alexandrian astronomer 
Ptolemy, entitled 'H MaOrjpaTucr} 2vvra£is, which, after 
the Arabians, is usually called The Almagest, Ptolemy, 
principally known from the system of the world which 
bears his name, died early in the reign of the Emperor 
Aurelius, which commenced in a. d. 161. 

The greatest of Arabian astronomers was Albatenius 
(so called from his birthplace, Baten, in Mesopotamia), 
who flourished in the ninth century of our era. About 
a century later the Persian astronomer Al-Sufi formed 
a catalogue of stars from his own observations. An- 
other catalogue was made by, or rather under the 
auspices of, the Mongol prince Mirza Mohammed 
Taraghai, or Ulugh Begh (as he is generally called), 
grandson of the famous Timour, from observations at 
Samarkand about a. d. 1433. 

The labors of Peurbach and Muller (usually called 
Regiomontanus) , toward the end of the same century, 
prepared the way for Copernicus, who showed the 
simple explanation of the planetary motions which 
resulted from supposing the Sun to be placed in the 
centre of the system. His work, De Revohitionibus 
Orbium Ccelestium, was published in 1543, in which 
year the illustrious author died. The foundation of 
the true theory of the solar system was thus laid, but 
the time for its establishment had not arrived. It was 
rejected by the great Danish astronomer, Tycho 
Brahe, in favor of a system called from him the 
Tychonic, in which the Moon and Sun were supposed 
to revolve round the Earth, and the planets round the 
Sun. Tycho's observations, however, furnished the 
means by which, less than 20 years after his death, 
Kepler deduced the laws of planetary motion. It 
was in 16 18 that he discovered his third and last 



Outline History 1 1 

law, which shows the mutual correspondence existing 
between the motions and distances of all the planets, 
and proves (though it was reserved for the genius of 
Newton to demonstrate this consequence) that they 
obey the same law of force directed toward the Sun. 




COPERNICUS (147 3-1 543) 

Meanwhile Galileo Galilei, equally famous, had 
been discovering a system of moons revolving round 
Jupiter as the planets do round the Sun, confirming 
by that and by other discoveries the truth of the Coper- 
nican system, and establishing the laws of motion, 
without a knowledge of which farther progress in 
astronomy as a science was impossible. Galileo died 



12 Stars and Telescopes 

in 1642; and in the same year was born Newton, 
the prince of philosophers, who discovered the law 
of gravitation, and demonstrated its competency to 
explain the most important of the lunar and planetary 
motions. This was made possible by the French 
astronomer Picard's determination of the true size of 
the Earth, and by Flamsteed's observations of the 
Moon, commenced at Greenwich in 1676, the year 

after the founding of the 
~"^~ Royal Observatory there. 

/*S£ The P/i ilosophice Na tu ralis 

Principia Mathematica, 
Newton's great work, was. 
published in 1687. 

Of the satellites of Sat- 
urn, Huygens discovered 
one, and Cassini four, in 
[- Jjj the latter part of the 17th 

century; and Huygens had 
explained the ring-like na- 

^*^ — - --- — — ture of the appendage to 

galileo ( 1 564-1 642) Saturn, the existence of 

which had been first no- 
ticed by Galileo. It was not until some time after the 
death of Newton in 1727 that his theory was further 
developed, and shown to be capable of explaining not 
only the principal courses of the planets, but the 
smaller deviations in their movements. This is due 
to the labors of several eminent mathematicians, but 
especially to Lagrange and Laplace. The Mecanique- 
Analytique of the former was published in 1787, and 
the Mecanique Celeste of the latter was completed in- 
1825. 

Toward the end of the 1 8th century arose an astron- 



Out I iiic History 13 

omer, Hanoverian by birth and English by adoption, 
who, by the discovery of Uranus in 17S1, not only 




SIR WILLIAM HERSCHEL'S 40-FT. TELESCOPE 
[Inscribed to his Royal Patron* King George the Third, 1795) 

extended what had previously been supposed to be 
the boundary of the solar system, but who, turning 
upon the sidereal heavens with unwearied diligence 
the powerful instruments constructed by himself,. 



n 



Stars and Telescopes 



acquired for mankind a knowledge of the distribu- 
tion and motions of the stars, which inaugurated a 
new era in the history of astronomy. Sir William 
Herschel, elected in 1820 the first president of the 
Royal Astronomical Society, died two years subse- 
quently. That Society published in 1827 a compiled 



SIR WILLIAM HERSCHEL (1738-1822) 



catalogue of stars, which was the standard work of 
reference on the subject until superseded by the cata- 
logue of the British Association containing 8,377 stars, 
published in 1845. 

Soon after this the boundary of the solar system 
was still farther enlarged by the famous discovery of 
Neptune in 1846; and the year following, Sir John 
Herschel published the results of his observations at 



Outline History 15 

the Cape of Good Hope, where he had devoted some 
years to diligent scrutiny of the stars and nebulce visi- 
ble only in the southern hemisphere, — a research 
similar to that in the northern heavens, initiated by 
his father and extended by himself and others. 

Early in the present century four new planets were 
discovered, the first of a group of many hundred 
revolving between the orbits of Mars and Jupiter, 
and so much smaller than all the others that distinct 
terms — planetoids or asteroids — were suggested for 
them. But as they differ from the other planets 
mainly in size, it is now more usual to call them 
small or minor planets. They remained four in num- 
ber until 1845, when a fifth was found. Since then, 
discovery has been so rapid that members of that 
group are now approaching 500 in number, and prob- 
ably there are hundreds more. The later discoveries 
cannot be seen without a powerful telescope, and 
nearly all the most recent were first recognized on 
photographic plates by D r Max Wolf of Heidelberg 
and M. Charlois of Nice. The number of known 
bodies of the solar system has been farther increased 
by the discovery in 1877 0I * two satellites revolving 
round Mars, and of the fifth satellite of Jupiter in 
1892. 

Also, the accurate observations of the last half cen- 
tury have enabled astronomers to determine the approx- 
imate distances of some of the fixed stars \ a Centauri, 
in the southern hemisphere of the sky, and about 
275,000 times more distant than the Sun, being, so 
far as is known, the nearest. 

It is now a third of a century since a new branch 
of astronomy was inaugurated by the analysis of 
the light of celestial bodies with the spectroscope. 



1 6 Stars and Telescopes 

This began with the investigations of Kirchhoff and 
Bunsen in 1859, which were brilliantly followed up by 
D r Huggins (at first in conjunction with Miller), and 
subsequently by Secchi, Janssen, Young, Lockyer, 
Vogel, Draper, Pickering, Maunder, and many 
others. Not only has the spectroscope enabled us 
to learn much of the chemical constitution and con- 
dition of celestial bodies both in and beyond the 
solar system, but its later developments have revealed 
motions of several of the stars in the line of sight (in 
some cases approaching, in others receding), which 
cannot be recognized in any other way. Likewise, 
the same instrumental method has led to the impor* 
tant discovery that many stars, although appearing 
single under direct scrutiny with the highest telescopic 
powers, are really double. One very interesting dis- 
covery of spectrum analysis is that the light of many 
of the nebulae (the great nebula in Orion, for exam- 
ple) does not proceed from multitudes of stars, as was 
once supposed, but from incandescent or intensely 
heated matter in a gaseous condition. 

The first person who is known to have noticed 
(though it is not unlikely Newton had done so 
before) a few of the dark lines crossing the prismatic 
spectrum at definite distances, was Wollaston in 1802, 
and he is known as their discoverer ; but as the accu- 
rate positions of a large number of them were first 
measured in 1815 by Fraunhofer, the celebrated 
German optician,, they are always called Fraunhofer 
lines. The measurement of the positions and dis- 
tances of these lines in the spectra of different celes- 
tial objects, and the comparison of the spectra of the 
heavenly bodies with the spectra of incandescent ter- 
restrial substances, have led to the important discov- 



Outline History 



17 



eries alluded to above. But the spectroscope is not 
the only new engine of astronomical research intro- 
duced in recent years. The application of photog- 




I 



FRAUNHOFER (1787-1826) 

raphy to celestial observations, and the instruments 
for making exact determination of the comparative 
amounts of light from different heavenly bodies have 
both inaugurated new fields of study which have borne, 
and are bearing, the richest fruit. 



S Si T- 



1 8 Stars arid Telescopes 

Jablonow, De Astronomies Ortu ac Progressu, etc. (Rome 1763), 
Lalande, Astronomie (Paris 1792). 

La Place, Exposition du Systhne du Monde (Paris 1800). 
Montucla, Histoire des Mathematiques (Paris 1802). 
Lalande, Bibliographie Astronomique avec V Histoire dt 

VAstro7W7nie (Paris 1803). 
Bailly, Histoire de V Astronomie Ancienne et Moder?ie (1805). 
Delambre, Histoire de V Astronomie Ancie)ine (Paris 181 7). 
Delambre, Histoire de V Astronomie die Moyen Age (Paris 18 19). 
Delambre, Histoire de V Astronomie Modeme (Paris 182 1). 
Delambre, Histoire de V Astronomie du XVIIP Siecle (1827). 
La Place, Precis, de V Histoire de V Astronomie (Paris 1S21). 
Bentley, Hindu Astrono??iy (London 1825). 
Rothmann, History of Astronomy, ' Library of Useful Know- 
ledge' (London 1832). 
Narrien, Origin and Progress of Astronomy (London 1833). 
Jahn, Geschichte der Astro?wmie (Leipzig 1844). 
Grant, History of Physical Astronomy (London 1852). 
Main, History of Astronomy, 8th edition of Encyclopedia; 
Britannica, vol. iii. (1853) ; 9th ed. ii. (1875), 744 (PROCTOR). 
Loomis, Recent Progress of Astro?io??iy (New York 1856). 
LEWIS, Astronomy of the Ancie?its (London 1862). 
BlOT, Etudes sur PAstrono??iie Indienne et Chi noise (Paris 1862), 
Wolf, Geschichte der Astronomie (Munich 1877). 

Houzeau, Bibliographie Generate, i. (1887), Introduction. 

Young, ' Ten Years' Progress,' A T ature, xxxv. (1887), 67, 86, 117. 

Bertin, ' Babylonian Astronomy,' Nature^ xl. (1SS9), 237, 261,. 
285, 360. 

Epping and Strassmayer, Astronomisches aus Babylon (Frei- 
burg 1889). 

Wolf, Handbuch der Astronomie, i. (Zurich 1890). 

Clerke, History of Astrono??iy during the XlXth Century 
(London 1893). 

Tannery, Recherches sur V Histoire de V Astronomie Ancienne 
(Paris 1893). 

Lockyer, The Dawn of Astrono?ny (New York 1894). 

Berry, Short History of Astronomy (New York 1899). 

Excellent chronological tables of salient events are in the 

Annuaire of Brussels Observatory (1877), p. 52, Chambers's 

Astronomy, vol. ii. p. 468, and in Miss Clerke's History, p. 

531. Consult, also, the extensive lists of Houzeau's Vade 

Mecum de VAstronome, ch. ii. pp. 34-147, a work of invaluable 

assistance in all investigation of the origins of astronomy, and 

its development down to modern times. — D. P. T. 




BAILLY (i736" I 793) 

(Jean SYLVAIN Bah.lv, a lear?ied astronomical writer and historian, was 
honored with the presidency of the National Assembly of 1789, and the 
mayoralty of Paris, i?i which capacity he served with sterling integrity. 
Besides his ' Histoire de V Astronomic,' in fi?'e volumes, he published 
many elaborate treatises, and held the high honor of membership i?i the 
three French academies simultaneously) 




DELAMRRE (1749-1822) 

(Jean Joseph Delambre was perhaps the most prolific of all French 
astrcmomical writers. Herschel's discovery of Uranus in 17S1 first 
gave him opportunity for distinction by constructing tables of the new 
planet's motion. He was collaborateur with Mechain in measuring 
an arc of meridian, and succeeded Lalande in 1S07 at the College de 
France. Del am BRB was an officer of the Legion of Honor) 



CHAPTER II 

THE EARTH 

HP HE general shape of the Earth on which we live 
*■ is that of a sphere or globe. Although the irreg- 
ularities of its surface present in places what appear, 
to our eyes, enormous elevations, the altitude of the 
highest mountain does not really amount to nearly 
the thousandth part of the diameter of the Earth ; 
and the depth of the lowest sea-bottom is about the 
same as the height of the highest mountain. 

But while our powers of locomotion are thus con- 
fined within so comparatively small a part of the 
vast universe of creation, the wonderful sense of sight 
has enabled us to acquire, through the agency of light, 
some knowledge of other bodies around us. Many of 
them are seen to be in motion, though it has been 
discovered that these movements are not all real, but 
in part apparent, produced by real motions of the 
Earth itself. All our knowledge respecting these bod- 
ies is embraced under the term astronomy ; and as 
that science has taught us to consider the Earth itself 
as one of the moving bodies of the universe (one of 
the planets, in fact, revolving round the Sun, from 
which they derive their light and heat), a knowledge 
of its motions, as well as of its shape and size, forms 
also an important part of astronomy. 

The Earth's actual form is not spherical, but slightly 
flattened at the poles, — the diameter taken anywhere 



20 Stars and Telescopes 

across the equator measuring 7,926.6 miles, and the 
polar diameter, or that taken from pole to pole, 7,901.5 
miles, 25 less than the equatorial. 1 

On the polar diameter as an axis the Earth rotates 
from west to east, while revolving in the same direc- 
tion in an orbit round the Sun. The axis of the Earth 
is inclined to the plane of this orbit at an angle of 66° 
32' 52".o (in 1900), and its rate of increase is nearly 
o"-5 annually. The true period of axial rotation is 

1 The Clarke spheroid of 1878, generally adopted, gives 
more exactly: — 

r Equatorial semi-diameter = 20,926,202 feet = 6,378- 

Earth's \ 3 ° X metres == 3.963.296 miles. 

I Polar semi-diameter = 20,854,895 feet = 6,356,515 
I metres = 3,950.738 miles, 

the polar compression being 2T^.T6- This supposes that the 
figure of our globe corresponds to an oblate spheroid, its equa- 
tor being a circle. But it is found that all existing measures 
of the Earth are better represented if the equator is regarded 
as slightly elliptical ; in other words, the Earth is an ellipsoid 
with three unequal axes. The greatest equatorial bulge lies 
very nearly coincident with Liberia on one side and the Gilbert 
Islands at its antipodes ; while the City of Mexico in the west- 
ern hemisphere and Ceylon in the eastern mark the meridian 
of least eccentricity. A good notion of the refinements in 
modern geodetic work is conveyed by stating that this investi- 
gation places Ceylon only 1,500 feet nearer the Earth's centre 
than Liberia ; farther observations are, however, necessary to 
establish this conclusion beyond dispute. But owing to the 
irregular past action of forces operant in moulding the Earth's 
crust, it is wholly unlikely that our planet has the general out- 
line of any mathematical solid; so that it becomes the business 
of the geodesist to assume the most probable figure, and then 
measure the deviations of the actual Earth or geoid therefrom 
in every particular. It is to be expected that the extensive 
series of pendulum observations now conducted by represen- 
tative nations will tentatively determine, not only the Earth's 
general figure, but all local deviations, with greater accuracy 
than the processes of the ordinary geodesy. — D. P. T. 



The Earth 21 

called a sidereal day ; it is divided into 24 sidereal 
hours, and is equal to 23 11 56 m 4 S .09 of ordinary time. 
But, the convenience of life rendering it necessary 
to regulate our time by the Sun, the day of our ordi- 
nary reckoning is a solar day, and this also is sub- 
divided into 24 equal parts called solar hours. The 
reason for the two kinds of day will be seen on reflect- 
ing that the Earth's actual motion round the Sun (or, 
what is in effect the same thing, the apparent motion 
of the Sun among the stars) places it a little farther east 
every day. Evidently, then, the Earth, rotating east- 
ward also on its axis, and having completed an entire 
rotation referred to the stars, must turn a little farther 
to complete an entire rotation referred to the Sun. 
The solar day, therefore, is longer than the sidereal 
day ; and these apparent solar days were employed as 
a measure of time in France until 18 16. But they are 
inconvenient for this purpose because of their unequal 
length, which is due partly to variations from day to 
day in the Sun's apparent motion among the stars. 
In practice, a mean or average day for the whole year 
(called the mean solar day) is now used, and the dif- 
ference between the mean and the apparent solar time 
at any instant is termed the equation of time. 2 The 

2 Coincidence of true Sun and mean Sun occurs four times 
annually; that is, the equation of time is then zero, and Sun 
and mean time clock agree. Following are the approximate 
days of each year when this takes place, also the dates when 
the equation of time is a maximum, either positive (Sun slow), 
or negative (Sun fast): — 
m 

12 February, Sun 14.5 slow. 

15 April, 0.0 

14 May, Sun 3.9 fast. 

15 June, 0.0 

Between these dates the equation of time is intermediate in 



25 July, 


Sun 


6.2 


slow. 


31 August, 




0.0 




1 November, 


Sun 


16.3 


fast. 


24 December, 




0.0 





22 



Stars and Telescopes 



mean solar day is universally accepted as the elemental 
unit of time in all other astronomical measurements of 
duration, and for the purposes of civil life as well. 

Of these mean solar days the Earth occupies 
365.25636 (equal to 365 d 6 h g m 9 s .o) in revolving 
round the Sun, and this period is called the sidereal 
year, because at the end of it the Earth is in the same 
position with respect to the Sun and the stars. But, 
just as the conveniences of life lead us to regard as 
the day not the precise period of time in which the 
Earth completes one ro- 
tation on its axis rela- 
tively to the stars, so do 
they not allow us to 
adopt as the year the 
exact period of time in 
which the Earth revolves 
in its orbit round the 
Sun. For what makes 
the observance of the 
year necessary to us is 
the change produced by 
the variations in the sea- 
sons ; and in conse- 
quence of a slow conical 
movement of the Earth's 
axis (occupying about 
25,800 years to com- 
plete a whole round, and 
called precession of the equinoxes, from the effect it 
produces upon the equinoctial points), the tropical 

value, and The Ephe??ie7'is i or Nautical Almatiac, for the par- 
ticular year must be consulted to find the precise amount at 
noon each day. — D. P. T. 




POSITION OF THE VERNAL EQUINOX 
B. C 2170 




TO INDICATE THE PRESENT POSITION 
OF THE VERNAL EQUINOX, NOW 
PASSED BEYOND TAURUS AND> 
ARIES 



The Earth 23 

year, in which all the changes of the seasons are 
run through, is 20" -\r-5 shorter than the sidereal 
year. In fact, the true length of the ordinary, or 
tropical year, is 363 d . 24219, or 363 d 5 11 48™ 45 s -5. 
It is now apparent that the Earth has three prin- 
cipal motions: (1) a rotation of the globe round its 
own axis, (2) a revolution round the Sun, during which 
the axis remains nearly parallel to itself, and (3) a 
slow conical motion of the axis so performed as to 
retain nearly the same inclination to the plane of the 
orbit throughout. But it should be mentioned that the 
axis is subject to an oscillation, in a period of a little 
less than 19 years, which alternately increases and 
diminishes the inclination by a small amount. This 
is called nutation, and was discovered in 1747 by 
Bradley, the third Astronomer Royal. 3 

3 Recent investigation has brought to light still another 
motion of the Earth which causes a periodic variation in the 
latitude of all places on its surface. An early research of 
Euler demonstrated that if a ' free rigid oblate spheroid ' 
(then supposed to represent what was known about the Earth) 
be set in rotation round an axis making a small angle with its 
axis of figure, and be not acted on by any force, the position of 
the axis of rotation within the spheroid will describe a circular 
cone round the axis of figure with a uniform motion, This 
principle applied to the Earth gave a theoretic period of about 
306 days, and the eminent German astronomer, C. A. F. Peters, 
was the first to discuss the question whether observations were 
sufficient to reveal a corresponding variation in terrestrial lati- 
tudes. Later the investigations of Nyr£n and others showed 
that if an inequality of this period existed at all, its amplitude 
could not exceed a few hundredths of a second — that is, a few 
feet on the surface of the Earth. As, however, the Earth is 
not a perfectly rigid spheroid, but is partly covered by a fluid 
envelope, and has perhaps the elasticity of steel (to adopt the 
conclusion of Lord Kelvin), Professor Newcomr finds the 
theoretic period not 306, but 441 days — a remarkably good 



24 Stars and Telescopes 

The mean density of the Earth is about five and a 
half times that of water ; which shows that some por- 
tion at least of the interior must be much denser than 
that of the exterior crust. The entire surface area of 
our planet is about 197,000,000 square miles. Of this 
about three fourths, or 145,000,000 square miles, are 
covered by water : and the fact that the area of water 




in the southern hemisphere is larger than that in the 
northern proves that the former portion of the Earth 
is somewhat denser than the latter, enabling it to retain 
the larger bulk of water. If the globe be divided into 
two hemispheres such that the surface of one contains 
the largest possible amount of land, and the other the 

agreement with the period of 427 days determined from ob- 
servation by M r Chandler in 1892. Professor Newcomb 
regards this agreement as affording conclusive and independent 
evidence of the rigidity of our globe ; and we may, he says, 
accept the conclusion that the pole of rotation of the Earth 
describes a circle round its pole of figure in about 427 days, 
and in a direction from west toward east, as a result of dynami- 
cal theory. Observations still in progress (1899) at Tokyo, 
Kasan, Pulkowa, Prague, Potsdam, Lyons, Philadelphia, and 
elsewhere, have revealed the exact nature of the polar oscilla- 
tion since 1890, as in the opposite diagram, and defined its mo- 
tion in the future. The curve is mainly elliptical rather than 
circular, and the extent of fluctuation is about 60 feet. — D. P.T. 





a a & 



00 


.„ 


(d 





1 


S 




«-5 




1 


.3 


a* 


« 


e 


\ 


.-§, 


i 


2 


6N 




1 


* 


■8 


s, 


5 




It 


9 


■i 


I 






g 

Id 


'5 .K 

PI 


v. 









Si 


V 




<^ 


< 


< 




q 




V 




Q 


V 

v. 


I 


S 








Id 

■J 




i 


-? 


■3 




•? 


4t 




9 






fi 






9 


;J5 




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l<va 



The Earth 25 

largest possible amount of water, the pole of the 
former portion will be very near the British Islands, 
and the pole of the other very near New Zealand. 

Form and Size 

ToDHUNTER, History of the Mathematical TJieories of Attraction 

and the Figure of the Earth. 2 vols. (London 1873.) 
Clarke, Geodesy (Oxford 1880). 

Woodward, American Journal Science, exxxviii. (18S9), 337. 
Preston, 'Pendulums, Am. Jour. Science, cxl\. (1891), 445. 
Cork, J. II., Geodesy (Boston and New York 1891). 
FOWLER, 'Measurement of Earth/ Knowledge, xx. (1897), 148. 

Invariability ok Rotation and Variation of Latitude 
NEWCOMB, American Journal Science, cviii. (1874), 161. 
Newcomb, Astron. Papers American Ephemeris, i. (1882), 461. 
GLASENAPP, Downing, The Observatory, xii. (1889), 173, 210. 
Chandler, The Astronomical Journal, xii., xiv. (1891-94). 
NEWCOMB, Month. Not. Royal Astron. Society, lii. (1892), 336. 
Doolittle, Proc. Am. Assoc. Advancement Science, xlii. (1893). 
Ball, ■ Wanderings of North Pole,' Smithsonian Report 1893. 
Woodward, The Astronomical Journal, xv. (1895), 65. 
Albrecht, Astronomische Nachrichten, cxlvi. (1898), 129. 
Chandler, The Astronomical Journal, xix. (1898), 105. 

Aurora Borealis, Terrestrial Physics, etc. 

Lovering, Mem. and Trans. Am. Acad. Arts and Sci. y 1867-73. 

Huxley, Physiography (London 1882). 

Tromholt, Under the Rays of Aurora Borealis (London 1885). 

Lemstrom, VAurore Boreale (Paris 1886). 

Bishop, 'Sky glows,' Warner Observatory (Rochester 1887). 

Symons, The Eruption of Krakatoa (London 1888). 

Ball, ' Krakatoa/ I?i Starry Realms (London 1892). 

Wallace, 'Our Molten Globe/ Fortu. Rev., lviii. (1892), 572. 

Mill, The Realm of Mature (New York 1892). 

King, 'Age of the Earth/ Smithsonian Report 1893, P- 335- 

Becker, ' Interior of Earth/ North Am. Rev., clvi. (1893), 439- 

vev, The Story of our Planet (London 1893). 
Kelvin, Popular Lectures and Addresses, ii. (New York 1S94). 
Dawson, Sal 1 en t Points in Science of Earth (New York 1894). 
Ax got, Les Aurores Polaires (Paris 1895). 

For Earth's density, tides, etc., consult Harkness, Washing- 
ton Observations 1885, App. iii. pp. 159 and 161 ; and GORE, 
1 A bibliography of Geodesy/ Report U. S. Coast Survey 1SS7 ; 
also Poole's Indexes, vols, i.-iv., and Astrophysical Journal, 
i.-viii. (1895-98).— D. P. T 



CHAPTER III 

THE MOON 

T N its annual journey round the Sun, the Earth is 
-*■ accompanied by a smaller body called the Moon ; 
her movement relatively to the Earth being in the 
nature of a motion in an elliptic orbit round the lat- 
ter, she is considered as a satellite or secondary planet 
thereto. 

The Moon, then, being by far our nearest neigh- 
bor among the heavenly bodies, much more has been 
learned about her than about the others ; selenog- 
raphy, in fact, has of recent years become almost 
a science of itself. The great work of Beer and 
Madler upon the Moon was published in the year 
1837, that of M r Neison (now M r Nevill) in 1876. 

On account of the Moon's proximity to us, an 
exact knowledge of her apparent motion among the 
stars is of the greatest practical use in navigation, 
thereby enabling the mariner to find his longitude at 
sea. The difficulty of this problem, which has exer- 
cised the labors of many distinguished mathemati- 
cians, arises from the perturbations to which the 
Moon's elliptic motion round the Earth is subjected 
through the gravitating action of the Sun and the 
nearer or more massive planets. 4 By reason indeed 

4 Foremost among these investigators in the last half-cen- 
tury have been Hansen in Germany, Pontecoulant and 




HANSEN ( I 795-1874) 



(Peter Andreas Hansen itas one of the greatest mathematical 
astronomers of the \qtli century. His tables of Sun and Moon, 
although now nearly a half century old, are still the basis of com- 
putation by which all timepieces are regulated, a?id the ships of 
all nations guided. Twice he was honored by the award of the 
gold medal of the Royal Astronomical Society) 




-1S7: 



(Charles Eugene Delaunay was perhaps the greatest of modem 
French geometers. He succeeded Arago and Le Yerrier as 
director of the Paris Observatory. Delau nay's masterpiece en 
titled '■La Thcorie du MouvemetU de la Lioie ' is published in two 
quarto volumes of the ' Met/wires de I' Academic des Sciences dc 
V Inst it ut de France ' {Paris 1860-67) 



The Moon 27 

of the much greater mass of the Sun, he exerts a 

more powerful attractive force upon the Moon than 
the Earth does, although the latter is so much nearer. 
The mathematician might, therefore, take exception 
to calling the Moon a satellite of the Earth ; and she 
is certainly not so, in the full sense that the moons 
of Jupiter and Saturn are satellites of those planets. 
Still, as we have said, the Moon's motion, relatively 
to the Earth, is a motion round it ; she is connected 
with otir planet by an indissoluble tie, and, from her 
great benefit to us, will always be called ' our satel- 
lite,' exciting our gratitude and commanding our con- 
stant attention. 

The actual duration of the Moon's orbital motion 
round the Earth is 2j d 7 11 43™ n s .545; but here 
again convenience compels us to regard as a lunar 
month or lunation not this, the time of her sidereal 



Delaunay in France, Airy and Adams in England, and Pro- 
fessor Newcomb and M r G. W. Hill in America. Hansen, 
Delaunay, and Airy spent a goodly portion of their lives 
upon the intricate mathematics of the 'lunar theory,' as it is 
termed. However, the formation of final tables for predicting 
the Moon's motions is a task so prodigious that only one of 
these investigators (Hansen) arrived at this complete solution 
of the problem; publishing in 1857 his Tables de la Lune con- 
struites d'apres le principe Newtonien de gravitation Universelle. 
These, in conjunction with Professor Newcomb's Corrections, 
are now exclusively employed in calculating future positions of 
the Moon; and at the present time the error of prediction does 
not often exceed 4", while its average is half that quantity, or 
about xoVff P art °f tne Moon's breadth (that is to say, about 
two miles in space). The story of the labors of mathematicians 
in determining the 'secular acceleration of the Moon' (one out 
of nearly a hundred perturbations which derange its motion 
round the Earth) is told by Professor Newcomb in the intro- 
duction to his masterful work entitled Researches on the Motion 
<of the Moon (Washington Observations, 1875). — &- ^' ^ 



28 Stars and Telescopes 

revolution, but the mean period between successive 
conjunctions with the Sun. This period is some- 
times called a synodic revolution, and amounts to 
2 9 d i2 h 44 m 2 S .684 ; upon it of course depend the 
Moon's phases as presented to the Earth, her illumi- 
nation being due to the light of the Sun. The Moon 
also receives solar light reflected from the Earth; 
and when the illuminated part of our globe turned 
toward her is the greatest (that is, near our New 
Moon) , this light is sufficiently strong to be reflected 
back again, enabling us to see the other part of her 
surface, as at Full Moon, only very faintly. This is 
popularly called ' the old Moon in the young Moon's- 
arms.' 

In consequence of the comparative proximity of 
our satellite, her distance and size can be determined 
much more accurately than those of any other heav- 
enly body. Her mean distance is 238,840 miles 
(the mean horizontal parallax being 57' 2".3) ; but 
her actual distance varies, in different parts of her 
orbit, between 221,610 and 252,970 miles. 5 The 
eccentricity of the Moon's orbit is 0.0549 : and its 
inclination to the ecliptic, or Earth's orbit, varies 
between 4 57' and 5 19', the mean value being 
5 8' 40". 

5 It is worthy of note that, while the Moon comes nearest 
to the Earth of all the heavenly bodies, the meteors alone 
excepted, its distance (about 60J), in terms of the radius of its 
primary body, exceeds that of all other known satellites in the 
solar system. Only Japetus, the outer satellite of Saturn,, 
approaches this maximum, its distance being 59.6 times the 
equatorial diameter of that planet; while the satellites nearest 
their primary, when estimated in like manner, are Phobos, the 
inner moon of Mars (2.8), and the newly-found satellite of Jupi- 
ter (2.6). — D. P. T. 




A PART OF THE MOON (WESTERN CENTRAL REGION) 

(From a photograph by the Brothers HBNRY at Paris, 23rd March 1S93. Age of the Moon, 
5 days 16 hours. The three large craters above the centre of the field are Theophilus 
(lowest one), Cyrillus, and Catharina ; and the diameter of cash is about 65 miles) 




SURFACE OF THE MOON, 1ST SEPTEMBER, 1S9O 
( Photograpfied at the L ick Observatory) 



3<D Stars and Telescopes 

The diameter of the Moon is 2,163 miles, or some- 
what less than two sevenths that of the Earth; so 
that the bulk of our planet is about 50 times as 
great as that of the Moon. But her density being 
little more than half that of our own globe, her mass 
amounts to only about fa that of the Earth. 

The Moon rotates on her axis very much more 
slowly than our Earth does. In fact, the duration of 
her rotation is exactly the same as the period of her 
revolution round the Earth. The consequence is 
that we always see precisely the same face of the 
Moon ; an entire half of her surface being always con- 
cealed from us, excepting such small portions of it 
near the visible half as come into view from libra- 
tions (as they are called), mostly produced by the 
varying velocity of her orbital motion and the incli- 
nation of her orbit to that of the Earth. 

That portion of the Moon's surface which we are able 
to see and study presents an appearance very differ- 
ent from that which any portion of the Earth's surface 
would do if similarly scrutinized. All indications show 
that there is no atmosphere surrounding the Moon ; 6 

6 The adjoining picture will serve to illustrate one of the 
critical indications referred to — the 
planet Jupiter in part hidden behind 
the limb of the Moon. No distortion 
of the delicate details of the planet's 
surface is apparent along the Moon's 
edge, as would be the case if the 
Moon had an appreciable atmos- 
phere. Planetary occultations are 
now excellently photographed. Lu- 
nar photography, begun by the elder JUPITER reappearing from 
Draper in 1840, and continued by occultation, 7 th Au- 
his son Henry, and by Ruther- gust i889 ( denning > 
furd, in New York, has culminated in splendid series of 





THE Moo.N NEAR FIRST QUARTER (LOEWV AND PUISEUX) 
(.From a photograph with the great equatorial Coude of the Paris Observatory) 



The Moon 31 

or at least that if there be any, it must be of exces- 
sive tenuity, and unable to hold clouds, or any ap- 
preciable amount of aqueous vapor, in suspension. 
Indeed, if there be any water on the surface of our 
satellite, it can only be very trifling in amount, and 
confined to the lowest depressions. Yet there is 
decisive evidence of the action of water on the lunar 
surface in bygone ages, so that this has probably in 
the course of time been all absorbed into the interior, 
or has by degrees become chemically combined with 
the solid material of the exterior. 

The surface is diversified by a large number of 
crateriform cavities (many of them containing a coni- 
cal hill at the bottom), and extensive arid plains. 
The latter retain the name of seas, given them when 
selenography was in its infancy, and when it was erro- 
neously thought that they were large bodies of water. 
Markings of a very peculiar character have also been 

negatives procured with the 13-inch Harvard telescope on 
Mount Wilson, California, and with the 36-inch telescope of the 
Lick Observatory. At the Columbian Exposition, Chicago, 
1S93, were exhibited many superb enlargements of portions of 
the moon from both series, some of the Harvard prints being 
on a scale corresponding to a lunar diameter of 14 feet. Many 
of the Lick originals (of nearly six inches diameter) are tech- 
nically perfect enough to bear enlargement to six feet ; while 
M. Prinz of the Royal Belgian Observatory has made photo- 
graphic amplifications of the lunar crater Copernicus from 
these negatives to a scale on which the Moon's diameter 
would exceed 30 feet. The finest photographs rival the clas- 
sic handiwork of Madler, Schmidt, and Lohrmann, but are 
secondary in this, that the very small craters are sometimes 
indistinctly registered by photography. Also the Lick nega- 
tives of the Moon have been industriously studied by Professor 
Weinek of Prague, who appears to have discovered new rills 
and craters, and has elaborated a beautiful series of enlarged 
drawings, which, reproduced by heliogravure, form very perfect 
detail pictures of lunar scenery. — D. P. T. 



32 Stars and Teles cQpes 

noticed in comparatively recent times, consisting of 
long whitish streaks running across other formations. 
These are called rills, and are usually supposed to be 
the results of crackings in the surface ; but it has been 
suggested that they may be dried water- courses. 7 

7 The ordinary surface structure of the Moon, apparently 
volcanic in the main, is best seen at or near the time of quad- 
rature, under oblique illumination. But the lunar rills or 
streaks, difficult to observe when the shadows of the mountains 
are most conspicuous, and very prominent when these shadows 
are imperceptible, demand a front illumination for their visibil- 
ity. Theoretically, the material of the streak-surface must, as 
pointed out by D r Copeland, be made up of multitudes of 
surfaces more or less completely spherical, but either concave 
or convex; and he therefore regards the streaks as produced 
by a material pitted with minute cavities of spherical figure, or 
strewn with minute solid spheres. On critical investigation of 
the rill systems (with a 13-inch telescope, at an elevation of 
8,000 feet, at Arequipa, Peru), Professor W. H. Pickering 
finds that the streaks of the system surrounding Tycho and other 
craters radiate, not from the centre of the ring mountains, but 
from a multitude of craterlets upon their rims. Also there are 
not, as heretofore supposed, any streaks hundreds or even thou- 
sands of miles long ; but their usual length varies from ten to 
fifty miles, while they seldom exceed one quarter mile in breadth 
at the crater. In the volcanic region surrounding Arequipa, 
the roads are, in some places, partially covered with a white 
pumice-like material, and its behavior under different inclina- 
tions of the line of illumination to the line of vision has led 
Professor Pickering to a conclusion quite identical with that 
of D r Copeland, that the general appearance of the streaks 
is most readily explained by the hypothesis of a light-colored 
powder extending away from the craterlets. The only farther 
step necessary to a satisfactory explanation of these mysterious 
markings is a reasonable elucidation of the process by which this 
powder has come to be radially disposed. Wurdemann's the- 
ory, cited by D r Gilbert in his address on ' The Moon's Face: 
a Study of the Origin of its Features ' {Bulletin Philosophical 
Society of Washington, xii. 285), is that meteorites, striking the 
Moon with great force, have splashed whitish matter in various 
directions, — which seems plausible. — D. P. T. 



The Moon 33 

Guillkmin and MITCHELL, The Moon (New York 1S73). 
Proctor, The Moon; her Motions, Aspects, etc* (London 1873). 
Rosse, Bakerian Lecture on 4 Radiation of Heat from the 

Moon/ in Philosophical Transactions for 1873, P 5^7- 
NASMYTH and CARPENTER, The Moon (London 1S74). 
NEISON, The Moon, and . . . its Surface (London 1876). 
Lohrmann, Mondcharte (Leipzig 1S7S). 
Schmidt, CharU der Gcbirge des Mondes (Berlin 187S). 
The Selenographical Journal (a London monthly, begun in 1878). 
Opelt, Der Mond (Leipzig 1879). 

Harrison, Telescopic Pictures of the Moon (New York 1SS2). 
LaNGLEY, ' Temperature of the Moon/ Mem. Nat. Acad. 

Sciences, iii. (1SS5) ; iv. (1SS9) with bibliography. 
Struve, L., Total Lunar Eclipses, 1S84 and 1S88 (Dorpat 18S9 

and 1893), giving for the lunar semidiameter 15' 32" 65. 
Rosse and Boeddicker, ' Lunar Radiant Heat,' Sei. Trans. 

Royal Dublin Society, iv. (1S91). 
Very, ' Distribution of Moon's Heat, and its Variation with 

Phase,' Utrecht Society of Arts and Sciences, 1S91. 
Webb and Espin, Celestial Objects (London 1893). 
WEINEK, Publications of the Lick Observatory, iii. (1894). 
Prinz, Agrandissenients des Photographies Lunaires (1894). 
Pickering, W. H., Ann. Harv. Coll. Obs., xxxii. pt. i. (1895). 
Elger, The Moon : description and map (London 1895). 
Loewy, PuiSEUX, Atlas Photographique de la Lune (Paris 

1S96-9S). 
Holden, Lick Observatory Atlas of the Moon (1897). 
Wei nek, Pkotographischer Mond- Atlas (Prague 1897-98). 
Schweiger-Lerchenfeld, Atlas der Himmelskunde (Vienna 

1S98). 
Herz, Valentiner's Handworterbuch der Astronomie (189S). 
Krieger, Mond- Atlas (Trieste 1S98). 
Very, ' Range of temperature,' Astrophys. Jour. viii. (189S), 199- 

So extensive is the popular literature of the Moon that 
reference only can be made to the ample lists of Poole's 
Index to Periodical Literature, vol. i. (1S02-1S81), pp. S65-S66 J 
vol. ii. (1882-1S86), p. 296 ; vol. iii. (1SS7-1S91), pp. 2S6-2S7 ; 
vol. iv. (1S92-1S96), p. 38 1. 

The scientific literature of the Moon occupies sixty-five 
pages of Houzeau and Lancaster's Bibliographic Generale de 
r Astronomic, vol. ii. (Brussels 1SS2), cols. 1185-1317. Consult, 
also chap. xiii. of HOUZEAU'S Vade Mecum de VAstronome 
(Brussels 1882) ; and the lists in The Astrophysical Journal ', 
1895-9S. — D. P. T. 

S & T — 3 



CHAPTER IV 

THE CALENDAR 

A LL those astronomical concepts which pertain to 
•l** the measurement of time having already been 
given, the relations of this important element to the 
concerns of ordinary life are now presented, as they 
obtain in the construction of the calendar. 

Originally the words almanac and calendar had the 
same meaning ; but, as often happens in such cases, 
usage has, in the course of time, given a slightly dif- 
ferent meaning to each of them. Almanac, as now 
understood, means an annual volume containing infor- 
mation of various kinds specially useful in the year to 
which it applies. Every almanac contains a calendar 
which gives in tabulated form for the year (divided 
into its months) the days of the week corresponding 
to each day of the month, with the dates of the prin- 
cipal anniversary days, and the times of the most 
important celestial phenomena, such as the rising 
and setting of the Sun and Moon, the Moon's changes, 
etc. i Almanac ' comes to us from the Arabic, ' al ' 
being the definite article in that language, and ' man- 
akh ' signifying a calendar. The word calendar is from 
the Latin calender, by which name the Romans called 
the first day of each month ; and this is probably 
derived from a word calare, to call (cognate with the 
Greek koXciv), because it was customary in very ancient 



The Calendar 35 

times to summon people together at the beginning of 

a month to make known the calendar arrangements 
for that month. 

Now it is evident that in distributing time its divis- 
ions must be made to correspond to those periodical 
celestial phenomena which regulate the course and 
ordinary actions of our lives. Most important of these 
is the day, or period of time in which the Earth, by 
revolving on its axis and turning successively toward 
and from the sun, causes the alternations of light and 
darkness. There is an unfortunate ambiguity in the 
word day, as it sometimes means the whole length of 
this revolution (arbitrarily divided into twenty- four 
hours, as there are no natural divisions except light 
and darkness), and sometimes that portion of it 
between sunrise and sunset. In all parts of the world, 
except the equatorial regions, the length of this varies 
considerably throughout the year. 

Besides the day there are two longer periods of 
time marked by celestial motions which are of great 
importance in the concerns of life. First of these is 
the year ; and the relation of the ordinary or tropical 
year to the sidereal year has already been given in 
Chapter 11. An astronomical year does not contain 
any exact number of days ; and the year in question, 
amounting to 363 d 5 11 48™ 45 s -5, is called the tropical 
year. As it w r ould be awkward to make a year con- 
sist of a number of days and a fraction of a day, the 
difficulty is got over by adopting in the calendar two 
years of differing lengths : one called a common year, 
consisting of 365 days, and an occasional one called 
a bissextile or leap year, embracing 366 days. This 
simple expedient keeps the designation of any part of 
the year in closer correspondence to the same state 



36 Stars and Telescopes 

of the seasons. By the old Julian reckoning, which 
erroneously supposed the year to contain 365J days 
exactly, each year which was divisible by four with- 
out remainder was considered a leap year, the extra 
day being added to the month of February. But by 
the Gregorian or present reckoning, adopted in Eng- 
land in 1752, the leap-year day is dropped at the end 
of each century, unless the centurial year is divisible 
by 400 without remainder — in which case the bissex- 
tile day is retained. For example, the years 1800 and 
1900 are not leap years, while the years 1600 and 
2000 are. 8 This further adjustment is equivalent to 
considering the year as consisting of 365.24250 days, 
thus making it differ by only 0.00031 of a day (or 
about 27 s ) from its true value, 365.24219 days. The 
accumulation of this small difference will not amount 
to an entire day for more than 3,000 years. 

The other natural division of time (called a month) 

8 Generally speaking, the number of days by which the Julian 
calendar differs from the Gregorian is as follows: — 

In the 15th century (1400- 1500), 9 days. 

16th century (1500-1600), 10 days. 
17th century (1600-1700), also 10 days, as 1600 

was a bissextile year. 

18th century (1 700-1800), 11 days. 

19th century (1800-1900), 12 days. 

20th century (1900-2000), 13 days. 

As the discovery of Columbus occurred in the 15th century, 
the day of the year on which it took place (12th October, Julian 
reckoning, or Old Style) falls nine days later in the Gregorian, 
or present reckoning (that is, 21st October, New Style). Russia 
still retains the Julian calendar ; and to avoid confusion, Russian 
dates are customarily written in fractional form, with the Old 
Style date as numerator : for example, 14th May (of any year in 
the 19th century) would be written May — ; and 5th September 
(Gregorian) becomes in Russia s^mberV ~" D ' P ' T ' 



The Calendar 37 

was suggested by the revolution of the Moon in its 
orbit; and, as already pointed out, it corresponds, not 
to the actual period oi the Moon's revolution round 
us referred to the stars, but to her revolution round 
the Earth as seen from the Sun. Evidently then the 
latter, called the synodic month, is the longer, because 
the Earth has been moving through a considerable 
portion of its orbit while the Moon has been going 
round it. The length of the synodic or lunar month, 
or a lunation simply, is 29 d i2 h 44™ 2 S .684 ; so that 
about I2.V lunations are completed in a year. But 
as it is desirable to divide the year into nearly equal 
portions, an integral number of which are completed 
at the end of each year, the months adopted in our 
calendar have no real relation to the period of the 
Moon's revolution, but are purely artificial divisions, 
each of which, excepting February, is a little longer 
than a lunar month. Some nations, the Hebrew peo- 
ples, for example, who attribute greater comparative 
importance to the lunar month than we do, actually 
employ it in their calendar, so that their year con- 
sists sometimes of twelve and sometimes of thirteen 
months. 

The fact is said to have been first noticed by Meton, 
a Greek astronomer, that 235 lunar months are very 
nearly equal to 19 tropical years. The former, in fact, 
contain 6,939 d i6 h 31™; the latter, 6,939 d 14 11 2 7 m . 
From this it results that during each 19th year of 
our reckoning the position of the Moon with refer- 
ence to the Sun will be very nearly the same on the 
same day of the year. Owing to the importance of 
this fact, the years were distributed into cycles of 19, 
each of which is called a Metonic cycle, and the num- 
ber of any year in this cycle is its Golden Number. 



38 Stars and Telescopes 

The year called by us b. c. i corresponded to the 
number one, and a. d. i to the number two in this 
cycle. As a cycle will be completed in 1899, the 
golden number of 1894, for example, is 14 ; and that 
of 1900 is 1, in the next period or cycle. 

The Sunday Letter, also termed the Dominical 
Letter, primarily of use in determining the date of 
Easter, is employed in ascertaining the day of the 
week on which any day of the year falls. To 
find the Sunday Letter of any common year, affix 
the first seven letters of the alphabet in their usual 
order to the first seven days of January ; then the 
letter adjoining Sunday is the Dominical or Sunday 
Letter of that year. If, for example, New Year's 
Day falls on Sunday, the Dominical Letter of the year 
is A ; if on Saturday, B ; if on Friday, C ; and so on. 
Manifestly, now, if every year contained only 364 days 
(364 = 52 X 7), all years would have the same Sun- 
day Letter perpetually ; that is to say, a given day 
of any month would always fall on the same day of 
the week. But as the common year contains 365 
days, it must always end on the same day of the week 
on which it began ; so that any year (whether common 
or bissextile) immediately following a common year 
must begin one day later in the week. Therefore its 
Sunday Letter falls one letter earlier in the alphabetic 
cycle. But the addition of the intercalary day at the 
end of February, and not at the end of the year, 
makes it usual to assign two Dominical Letters to 
each bissextile year; the reason for which may be 
illustrated by the following example : The year 1892 
beginning on Friday, its Sunday Letter is C. But 
the intercalary day, 29th February, disturbing the 
regular periodic succession of the common year, the 







S v 

V, $ 



1^ ^> 



u 






o 






•Ml 



33* 

*•! I 

•$*§ « 
s k ^ 

8^ § 

k § K 

§ 5 I 

6 






u 






f! 



40 



Stars and Telescopes 



i st March falls one day later in the week on that 
account ; so that the Dominical Letter for the re- 
maining ten months of the bissextile year evidently 
drops back one letter in the alphabetic cycle, — or 
leaps over one letter, whence the name ' leap year.' 9 



9 Easter day is given in the following table, together with 
the Golden Number, Dominical Letter, and the corresponding 
years of the Jewish and Mahometan Eras, with the day of the 
month in each ordinary year when they begin : — 



Year 


Easter 
Day 


Golden 
Num- 
ber 


Domin- 
ical 
Letter 


Jewish Era 


Mahometan Era 


Year 


Begins 


Year 


Begins 


1890 

1891 

1892B 

1893 

1894 

1895 

1896B 

1897 

1898 

1899 

1900 


6th April 
29th March 
17th April 

2d April 
25th March 
14th April 

5th April 
1 8th April 
10th April 

2d April 
15th April 


10 
11 
12 
13 
14 
15 
16 

17 
18 

«9 


E 

D 
CB 

A 

G 

F 
ED 

C 

B 

A 

G 


5651 
5652 
5653 
5654 
5655 
5656 

5657 
5658 

5659 
5660 
5661 


15th September 

3d October 
22d September 
nth September 

ist October 
19th September 

8th September 
27th September 
17th September 

5th September 
24th September 


1308 
1309 
1310 
1311 
1312 
1313 
1314 
1315 
1316 
1317 
1318 


17th August 

7th August 
26th July 
15th July 

5th July 
24th June 
12th June 

2d June 
22d May 
12th May 

ist May 



Other chronological data are printed each year in The Ameri- 
can Ephe?neris and Nautical Almanac. For farther information 
on calendars and chronology, consult the articles on these sub- 
jects in The Encyclopedia Britannica (9th edition), Ideler's 
Handbuch der Mathematischen und Technischen Chronologie, 
Chambers's Astronomy (4th edition),vol. ii. bk.io,and Schram's 
Hilfstafeln filr Chronologic Also, Mahler's Chronologische 
Vergleichungs-tabellen will be found helpful. More accessible 
doubtless is Bond's Handy- Book of Rules and Tables for Verify- 
ing Dates with the Christian Era, etc. (London 1869) ; also D r 
Wislicenus's Astronomische Chronologic (Leipzig 1895) ; and 
the article by the same author in Valentiner's Handworter- 
buch der Astroiiomie, i. (Breslau 1897). Lewis has a popular 
paper on Almanacs in The Observatory -, xxi. (1898). — D. P. T 



CHAPTER V 

THE ASTRONOMICAL RELATIONS OF LIGHT 

T T is essential to make early reference to the means 
by which the heavenly bodies become known to 
US through the agency of light, and to the effects of 
the motion of light upon their apparent places. 

The undulations, or light waves, are transmitted 
through a very rare but material substance, diffused 
through all space, to which the name ether has been 
given ; and to distinguish it from the chemical sub- 
stance with the same name, it is called luminiferous 
(that is, light-bearing) ether. The vibratory motions 
of the particles of this ether, called waves of light, 
when once originated by a luminous body acting as a 
source of light, are transmitted through the atmos- 
phere in its ordinary state, because it is permeated by 
these particles, and through some other substances 
called for this reason transparent. In passing from 
one transparent medium into another of different 
density, the rays of light, propagated originally in 
straight lines, are bent or turned in a direction in- 
clined to that previously followed. This bending is 
called refraction, and is greater, the greater is the 
difference of density of the different media through 
which the light is successively transmitted. It also 
varies according to the angle of inclination to the 
surface of a medium at which a ray of light enters it ; 



42 Stars and Telescopes 

the law being, that if the media be the same, the sine 
of the angle of incidence (whatever that angle be) is 
always in a constant ratio to the sine of the angle of 
refraction. This law was discovered about 162 1 by 
Willebrord Snell of Leyden. The ratio in any par- 
ticular case can only be determined by experiment. 

Rays of light coming to us from one of the heavenly 
bodies suffer a constantly increasing refraction in 
passing through the successive strata of the Earth's 
atmosphere, which are more and more dense the 
lower down they are. The general result can only 
be ascertained by astronomical observations, the celes- 
tial object appearing in the direction in which the 
ray of light proceeding from it enters the eye. The 
law just mentioned shows that a body exactly over- 
head, or in the zenith of any place, is seen in its true 
position, its rays having undergone no refraction at 
all ; and that the refraction is greater the farther the 
object is from the zenith, or the nearer it is to the 
horizon. Half-way between the two, or at an altitude 
of 45 , the refraction amounts to nearly 1'; at 20 
to 2^ '; at io° to 5 J' ; at 5 to 10' ; close to the 
horizon it is as much as 33' or 34', varying consid- 
erably with the temperature and pressure of the 
, atmosphere. As this arc is a little more than the ap- 
parent diameter of the Sun or Moon, it follows that 
when either of those bodies seems to be just above 
the horizon, it is really just below it, refraction always 
making a heavenly body appear higher above the 
horizon than it really is. 

That the propagation of light, whether it be a sub- 
stance, as was formerly supposed, 10 or an undulatory 

10 'It is possible/ says Clerk Maxwell, 'to produce dark- 
ness by the addition of two portions of light. If light is a sub- 



The Astronomical Relations of Light 43 

motion in a substance, as it is now known to be, 

should occupy time, seems a priori what might be 
expected. But so extremely rapid is this propaga- 
tion that the ancients, having no means of recogniz- 
ing it by astronomical observations, appear to have 

thought that it was instantaneous, which it practically 
is between places on the Earth's surface. The first 
person to discover that the velocity of its transmission 
is measurable was the illustrious ROMER of Copen- 
hagen in 1675, while discussing the observations of 
Jupiter's first satellite made by himself, and at Paris 
by CASSINI. He found that the intervals of time 
between successive immersions of the satellite into 
the shadow of the planet and its emersions therefrom 
were different according to whether the Earth in its 
orbital motion was approaching Jupiter or receding 
from it ; and he concluded that the cause of this 
was the Earth's motion combined with that of light, 
which was thus -recognized to be a sensible and meas- 
urable quantity. Romer's explanation of the differ- 
ences observed was contested by Cassini ; but it 
nevertheless gradually obtained general acceptance 
among astronomers, and about 50 years after its 
publication a most remarkable confirmation of its 
truth was obtained by the discovery of the aberra- 
tion of light. Romer's approximate determination of 
the time required by light in passing from the Sun to 
the Earth was rather more than eleven minutes ; but 
it is now known that when the Sun is at its mean 
distance, this interval is 498 s (8 m 18 s ), the best 
determinations of the velocity of light by the refined 

stance, there cannot be another substance which, when added 
to it, shall produce darkness. We are, therefore, compelled to 
admit that light is not a substance. ' 






PHOTOTACHOMETER FOR MEASURING THE VELOCITY OF LIGHT 
{View from above) 

{Only in the latter half of the jgth century was the velocity of light first meas- 
ured with accuracy. The favorite method is that of the ' Revolving Mirror] 
inaugurated i7i 1862 by Foucault, the eminent French physicist {page 47). 
Professor Michelson, now of the U?iiversity of Chicago, improved upon his 
viet hods in 1S78, and at IVashingtofi, in 1880-82, Professor Newcomb employed 
the greatly enlarged apparatus above shown, embodying farther important 
modifications. The speed of the revolving mirror, CD — a rectangular prism 
of polished steel about i\ inches square — was 250 turns in a second. The three 
piers supporting the instrument wer» about 7 feet apart ; and the stationary 
viirror reflecting the retur7i ray was nearly t.\ miles distant. For description 
of the apparatus and its use, and a fell discussion of the problem, see 'Astro- 
nomical Papers of the American Et>hemeris,'' vol. ii. {Washington i8qi). Also 
Cornu, ' Annates de VObservatoire de Paris? Memoires, xiii. (1876); Young 
a?id Forbes, ' Philosophical Transactions,'' 1882. For bibliography, consult 
* Washington Observations y for 1885, Appendix Hi. p. 153.) 



The Astronomical Relations of Light 45 



and accurate methods of modern physicists and 
astronomers {vide opposite page) giving 186,330 
miles a second. So that when, for example, we are 
observing Neptune (a planet 30 times more distant 
than the Sun), we see it by light which began its 
journey earthward somewhat more than four hours 
previously. 11 

A few words in conclusion on the aberration of light. 
In 1725-27, while making a number of careful obser- 
vations of y Draconis (a 
star which crosses the merid- 
ian in the south of England 
very near the zenith), in the 
hope of determining its par- 
allax and distance, Bradley 
was surprised to notice a reg- 
ular change in its apparent 
position. Its period, like that 
produced by a measurable 
parallax, was exactly a year ; 
but the amount was much 
greater than he had expected, 

and the direction was the reverse of that which would 
be caused by parallax. Speculating on the source of 

11 This quantity is technically termed the 'aberration-time/ 
and is equal (in seconds) to 498 times the planet's distance from 
the Earth expressed in astronomical units. The mean value 
of the aberration-time (between Sun and Earth) is the constant 
term in the 'equation of light/ Also there is an aberration of 
the planets due to their orbital motions in space. Suppose our 
globe to be at rest in its orbit ; the aberration of light would 
then vanish. But as a planet is always seen from the Earth in 
the direction where it actually was when light left it, obviously 
its absolute position at the time of observation must differ 
from the apparent position, because of (1) the aberration- 
time, and (2) the planet's orbital motion athwart the line of 




ROMER (1644-I7IO) 



4 6 



Stars and Telescopes 



this, it occurred to him that the Earth's motion round 
the Sun would lead to an effect of this kind when 
combined with the gradual propagation of light as 
discovered by Romer. Calculation confirmed this 

conjecture \ and the ab- 
erration of light (as 
this phenomenon is 
called) affords one of 
the methods by which 
the velocity of light was 
subsequently deter- 
mined. 

The nature of the 
apparent change in a 
star's place produced 
by aberration depends 
upon its position with 
respect to the plane 
of the ecliptic. If 
that position be in the 
plane of the Earth's orbit, the star will, in conse- 
quence, appear to change its place in a straight line 
only ; if it be nearly in the pole of the ecliptic, the 
star will appear to describe a circle round its true 
place ; while, if situate anywhere between the ecliptic 
and its pole, the change of apparent place will form 
an ellipse whose eccentricity is greater the nearer 
the star is to the plane of the ecliptic. The angular 




JAMES BRADLEY (1692-1762) 



sight. This is called planetary aberration. A similar but very 
small effect obtains for the Moon, amounting to about o".5, 
the linear value of which, at the distance of our satellite, is 
2,650 feet ; that is to say, while light is travelling from the 
Moon to the Earth (nearly I s . 3), the Moon advances about 
one-half mile eastward in its orbit. — D. P. T. 



The Astronomical Relations of LigJit 47 



semi-diameter of the circle in the former case, or the 
semi-major axis of the ellipse in the latter case, is 
practically a constant quantity, called the constant of 
aberration ; for the only circumstance that can make 
it vary is the change of the Earth's orbital velocity 
at its different distances from the Sun, and the pro- 
portion of this variation to the whole velocity is very 
small. The best modern value of the constant of 
aberration is 2o".40 2, determined by M. Nyrkx. 

The Earth's ro- 
tation on its axis, 
combined with the 
motion of light, 
also causes a phe- 
nomenon of a simi- 
lar kind, called the 
diurnal aberration. 
Its amount, of 
course, varies ac- 
cording to the lati- 
tude of the place 
of observation, be- 
ing greatest at the 
equator, where the 
velocity produced 
by the Earth's ro- 
tation is greatest, and smaller the nearer the poles 
are approached, at which points the diurnal aberra- 
tion vanishes. At latitude 40 , the average for places 
in the United States, the constant of diurnal aber- 
ration (for an equatorial star at meridian passage) 
amounts to o".24 ; the velocity of rotational transla- 
tion at latitude 40 being about the eighty-fifth part 
of the Earth's velocity in its orbit. 




Leon Foucault (1819-1868) 



CHAPTER VI 

THE SUN 

/^\N the Sun's distance depends our knowledge of 
^-^ all absolute magnitudes in the solar system ; for 
by Kepler's third law (page 93), the proportions of 
the distances of all the bodies moving round the Sun 
are known exactly from their periodic times of revo- 
lution : so that if the Earth's distance from the Sun 
be known, the distances of all the planets from the 
Sun and from each other can be deduced by a very 
simple piece of arithmetic. Also, the Sun's distance 
is of the first order of significance, because it is the 
elemental unit in our measures of the distances of the 
fixed stars. 12 To measure the Sun's parallax with pre- 

12 The Sun, cosmically speaking, is simply a star, but the 
nearest fixed star is 275,000 times more remote; so that the 
Sun's vastly greater brightness is, for the most part, due to mere 
proximity. Still, the distance of the Sun is by no means easy 
to conceive or illustrate. Recalling that the distance round the 
Earth's equator is about 24,000 miles, ten times this gives the 
distance of the Moon, which is practically inconceivable ; but 
the Sun is 390 times more remote. As the two bodies are 
about the same in apparent size, it follows that the Sun's actual 
diameter is about 390 (accurately 400) times greater than the 
Moon's. The diagram on the opposite page will not only con- 
vey a true idea of the relative size of Sun, Earth, and Moon, 
but by imagining spheres of the given proportions set at the 
distances indicated, the actual relations of these bodies in 
space may, in some sense, be comprehended. On the same 



RE LA TIVE SIZE OF SUN, EARTH &> MOON 
(On scale of iS,ooo miles = i inch.) 



THE EARTH 





Mean Distance from 
the sun, 429 feet. 

j On 1st Jan. 422 ft. 
\ On 1st July 436 ft. 



THE MOON 

O 
Mean* Distance from the Earth, 

I3i INCHES. 

At perigee, \ in. nearer. 
At apogee, \ in. farther. 



So 



Stars and Telescopes 



cision is difficult on account of the great distance of 
that body compared with the size of the Earth ; a 
small error in the measured parallax produces a large 
error in the resulting distance. 

From the time of Flamsteed (Astronomer Royal 
from 1675 to 1719) it has been known that the Sun's 
parallax does not exceed 10". Halley pointed out 

the advantage that 
might be gained by 
observing transits of 
Venus, those rare oc- 
casions when she 
passes at inferior con- 
j unction over the 
Sun's disk. Accord- 
ingly the transits of 
1 761 and 1769 were 
observed by a large 
number of parties 
sent to different re- 
gions of the world. 
But the solution of 
the problem in this 
manner is encompassed by practical difficulties. Many 
results were obtained by calculation from the observa- 
tions of the transits in those years ; but for a long time 
it was agreed among astronomers that the value of the 
Sun's parallax obtained by Encke in 1835, which 
amounted to 8".5 7, was the best. More recently 
many determinations, made by observing Mars at its 
closer oppositions, and by other methods, have shown 

reduced scale, the nearest fixed star would be 16,000 miles 
distant, equal to a journey from New York westerly to Japan 
and back. — D. P. T. 




Edmund Halley (1656-1742) 



The Sun 5 1 

that the Sun's parallax is greater by at least o".2 
than ENCKE'S value. Moreover, M r E. J. STONE, 
late of Oxford, pointed OUt that ENCKE'S discussion 

was affected by erroneous interpretations of some of 
the observations, and that, when these are rightly 
explained, they also give a value considerably larger. 
The observations of the more recent transits in 1874 
and 18S2 likewise prove to be most consistent with a 
value of about S".S4. ; but the method is now some- 
what discredited, as compared with other methods. 13 
From his skilful observations of Mars at Ascension 

13 The available methods of ascertaining the Sun's dis- 
tance, more than a dozen in number, may be divided into three 
classes: (1) by geometry or trigonometry ; (2) by gravitational 
effects of Sun, Moon, and planets; (3) by the velocity of 
transmission of light. The first includes transits of Venus, 
and near approaches of the Earth to Mars, or to small planets 
exterior thereto, — at which times the distances of these bodies 
from the Earth are not difficult to measure. Adopting, with 
Professor Young, the number 100 as indicating a method 
which would insure absolute accuracy, this class of determi- 
nations will range all the way from 20 to 90. The second class 
of methods, too mathematical for explanation here, depends on 
the Earth's mass, arid their present value may be expressed as 
40 to 70; but the peculiar nature of one of them (utilizing the 
disturbances which the Earth produces in the motions of Venus 
and Mars) offers an accuracy continually increasing, so that 
two hundred years hence it alone will have settled the Sun's 
distance with a precision entitled to the number 95. But the 
best methods now available are embraced in the third class, 
which employ the velocity of light (determined by actual physi- 
cal experiment, as related in the last chapter) ; and their present 
worth is about 80 or 90. The problem of the Sun's distance is 
one of the noblest ever grappled by the mind of man ; and no 
one of the numerous elements with which it is complexly inter- 
woven can yet be said to have been determined with the highest 
attainable precision. (Harkness, The American Journal of 
Science, exxii. (1SS1), 375 ;YoUNG, General Astronomy (Boston 

#), chapter xvii.) — D. P. T. 




A GROUP OF SUN SPOTS, SHOWING CHANGES IN EIGHT DAYS 

{Photographed by Rutherfurd) 



The Sun 5 ^ 

Island during that planet's favorable -opposition in 
1877, D r GlLL obtained a solar parallax of 8".7<S, 
which gives for the Sun's mean distance very nearly 
93,000,000 miles, — quite certainly within a quarter 
of a million miles of its true value. 14 

14 An admirable summary of investigation of the Sun's 
distance is given by D r GiLL as an introduction to M™ Gili/s 
Months in A scension (London, 1880), — an account of the 
expedition to that island three years previously. The value 
of the Sun's parallax, S' / .848 ± o".oi3, determined by Professor 
NEWCOMB ( Washington Observations, 1865), and now become 
classic, is adopted in all the national astronomical ephemer- 
ides except the French, which uses Le Verrier's slightly 
larger value. Independent determinations of this constant 
here given show the measure of modern precision in this im- 
portant field of research; and the relations of the values to 
each other will be apparent on recalling that the addition 
of o".oi to the Sun's parallax is equivalent to diminishing his 
distance about 105,000 miles : — 

rr it 

Velocity of Light 8.808 ± 0.006 
Contact and Micrometer Observa- 
tions, Transit of Venus, 1874 8.8 
American Photographs, Transit of 

Venus, 1874 8.883 ± 0.034 

Velocity of Light 8.794 
French Photographs, Transit of 

Venus, 1874 8.81 ± 0.06 
Brazilian Observations, Transit of 

Venus, 1882 8.808 
British Contact-Observations, Tran- 
sit of Venus, 1882 8.832 ± 0.024 
American Photographs, Transit of 

Venus, 18S2 8. 842 db 0.012 

Planetary Masses 8.795 - °oi6 

Lunar Occultations 8.794 — 0.016 

Transits of Venus, 1761 and 1769 8.79 ± 0.034 

Transits of Venus, 1874 and 1882 8.896 ± 0.022 

1 Opposition of ( <"> Victoria 8.801 ± 0.006 

I Small Planets (So) Sappho 8.798 ±0.0.1 

1 I (7) Ins 8.812 + 0.009 

A nearly complete list of the more important earlier papers 
is given in Newcomb's Popular Astronomy (Appendix). The 
newly discovered small planet 1898 DQ, at its near approach 
to the earth in 1900, is expected to yield a value of the Sun's 
distance far exceeding all others in precision (page 40S). 



(1SS0) 


Todd 


(1SS1) 


PUISEUX 


(1881) 


Todd 


(l8Sr) 


Newcomb 


(1885) 


Obrecht 


(1887) 


Cruls 


(1887) 


E. J. Stone 


(1888) 


Hark ness 


(1889) 


Harkness 


(1890) 


Battermann 


(1890) 


Newcomb 


(1891) 


Auwers 


(1892) 


Gill 


(1893) 


Gill 


(1898) 


Elkin 



54 Stars and Telescopes 

It must be noted, that in consequence of the eccen- 
tricity of the Earth's orbit (which amounts to 0.01677), 
the Sun's actual distance varies between a million and 
a half miles less, and a million and a half miles more 
than this. It is least about 1st January, when the Earth 
is at that end of the major axis of its orbit which is 
nearer the focus occupied by the Sun, and greatest 
about 1 st July, when the Earth is at the opposite end 
of that axis. These two points are called respec- 
tively the perihelion and the aphelion of the Earth's 
orbit. 

Accepting, then, 93,000,000 miles as the Sun's mean 
distance from us, it is easy to find, by observing his 
apparent diameter, that his real diameter is 865,350 
miles. This is nearly no times as great as the Earth's, 
so that the Sun's volume is able to contain the Earth's 
1,300,000 times over. But the comparative effects of 
their attractive forces show that the Sun's mass is only 
331,100 times as great as that of the Earth. Conse- 
quently his density must amount to only about one 

Professor Harkness published in 1891 a laborious paper 
entitled The Solar Parallax a?id its Related Constants (Washing- 
ton Observations, 1885), in which this quantity is treated, not 
as an independent constant, but as 'entangled with the lunar 
parallax, the constants of precession and nutation, the parallac- 
tic inequality of the Moon, the lunar inequality of the Earth, 
the masses of the Earth and Moon, the ratio of the solar and 
lunar tides, the constant of aberration, the velocity of light, 
and the light-equation.' Collating the great mass of astro- 
nomical, geodetic, gravitational, and tidal results which have 
been accumulating for the past two centuries, and applying the 
mathematical process known as a 'least square adjustment,' 
he derives the value 8".8o9 ± o".oo6, giving for the mean dis- 
tance between the centres of Sun and Earth 92,797,000 miles. 
A valuable bibliography of the entire subject concludes Pro- 
fessor Harkness's paper. — D. P T. 



The Sun 55 

fourth that of the Earth, or rather more than 1 \ times 
the density of water. 15 

The shape of the Sun appears to be that of a perfect 

15 Possible changes of the Sun's diameter from time to time 
have been critically investigated by D r Auwers of Berlin, and 
Professor NSWCOMB, with negative results; nor are the obser- 
vations yet made sufficient to disclose any difference between 
equatorial and polar diameters. The heliometer (p. 277) affords 
the best means of measuring the Sun's apparent diameter, 
or the angle subtended by its disk. The orbit of the Earth 
being elliptical, this diameter changes in the inverse proportion 
of the Earth's varying distance from the Sun ; at the beginning 
of the year it is 32' 32", and 31' 28" early in July, the mean 
value being 32' o". Supposing the form of the Earth's orbit 
unknown, daily measures of the Sun's varying diameter would 
alone, in the course of a year, enable the precise determination 
of the figure of that orbit, so accurately can these measures 
now be made. The linear equivalent of one second of arc at 
the Sun is 450 miles. The present uncertainty in the solar 
diameter does not much exceed 2"; that is to say, about 900 
miles, or approximately y^uo °i tne entire diameter. D r Au- 
wers' recent value of the semi-diameter is 15' 59"63. 

A simple relation between the Sun's mass and its dimen- 
sions relatively to the Earth enables us to determine that the 
force of gravity at the Sun's surface is 27! times greater than 
it is here ; so that while a body on the Earth falls only 16.2 feet 
in the first second of time, at the Sun its fall in the correspond- 
ing interval would be no less than 444 feet. If a hall clock were 
transported to the Sun, its leisurely pendulum would vibrate 
more than five times in every second. So great is the Sun's mass 
that a body falling freely toward it from a distance indefinitely 
great would, on reaching the Sun, have acquired a velocity of 
3S3 miles per second. The great Krupp gun exhibited at the 
World's Fair in 1893, ^ faed from Chamounix in the direction 
of Mont Blanc, at an elevation of 44 , would propel its projec- 
tile of 475 pounds in a curve meeting the earth at Pre-Saint- 
Didier, I2j miles from Chamounix, and whose highest point 
would be more than a mile above the summit of Mont Blanc. 
If we could suppose the same gun to be fired similarly on the 
Sun, so great is the force of gravity there that the projectile 
would be brought down to rest about half a mile from the 
muzzle. —Z> P. T. 



56 Stars and Telescopes 

sphere. As soon as he was observed through a tele- 
scope, it was seen that his surface is usually diversified 
by a number of black spots of varying dimensions and 
configurations. In 1 6 1 1 , John, son of David Fabricius, 
of East Friesland, first noticed their apparent motions 
across the disk, from which it became evident that 
the Sun is endued with a stately rotation on his axis. 
These motions are such as would carry an equatorial 
spot from first appearing on the Sun's disk to appear- 
ing there again (if persistent enough to do so) in 
about 2 7 days ; hence, taking into account the simul- 
taneous motion of the Earth in its orbit round the 
Sun, it was inferred that the Sun turns on his axis in 
about 2 5 d 7 h . It should be stated, however, that 
recent observations have shown that the spots nearer 
the Sun's equator move somewhat more rapidly than 
those farther from it. Spots are very seldom seen at 
a greater distance from the Sun's equator than about 
30 of solar latitude. These regions of the solar sur- 
face take as much as 26^ days to make a complete 
revolution. 16 



16 From groups of the faculse (pages 57-58) D r Wilsing has 
found that the Sun's equator revolves in 25 d .23 ; but these 
observations are exceedingly difficult, and a repetition of the 
work is desirable. Professor Young and D r Crew have deter- 
mined the period of rotation of the Sun's equator by means of 
the spectroscope, utilizing that technicality called Doppler's 
principle. This means that the spectra from opposite sides of 
the Sun (the east side coming toward the Earth, and the west 
receding from us) are brought into juxtaposition ; then, careful 
measurement of the difference in position of a given line in 
the two spectra forms the basis for calculating the rapidity of 
rotation. M. Duner of Lund, Sweden, carrying this research 
still farther, into high solar latitudes, finds for the equatorial 
regions a period of sidereal rotation equal to 25*. 46, in close 
correspondence with the determinations of Carrington and 



TJn Sun 57 

The periodicity of the sun spots was discovered by 
Schwabe oi Dessau in 1838. The subject has since 
attracted much attention, and the period, so far as 
it is constant, has been pretty accurately determined 
by WOLF of Ziirich to be a little more than eleven 
years ; but the physical cause of the periodicity is not 
yet satisfactorily explained. A recent epoch of maxi- 
mum abundance and frequency, more than usually 
protracted, was in 1883-84. The diminution being 
generally less rapid than the increase, a minimum 
followed in 1S89; the next maximum passed during 




THE SUN (from a photograph by RuTHERFURD) 
(Faculae are shown adjacent to tJie spots near the Sun's limb) 

Spoerer from the spots alone. The slowing down as the 
poles are approached is remarkably verified, his results giving, 
for the rotation period at latitude 75 , no less than 3S d -54. 
If. Duner's observations were made near the time of mini- 
mum spots, and it would be interesting to repeat the determi- 
nation near the epoch of maximum spottedness — D P. T. 



53 



Stars and Telescopes 



the latter half of 1894, and the next minimum may 
be expected early in 1900. 

The solar spots are thought to be produced by dis- 
locations in portions of the photospherical envelopes 
which surround the Sun, so that we see in them to a 
depth below that of the ordinary surface. 17 In their 
immediate neighborhood there are often to be seen 
patches of more than usual brightness (heapings up, 
so to speak, of luminous matter), which are called 
faculce, the Latin word for torches. Both phenomena 
indicate activity and commotion in the outer part 
(and to some unknown depth below) of the Sun's 
surface. 

17 The Sun, as seen with telescopes ot low magnifying power, 
is shown on the preceding page ; and page 52 illustrates admi- 
rably the changes taking place from day to day in an average 




SUN SPOT HIGHLY MAGNIFIED (SECCHl) 

{Observe that the Penumbra is darker nearer 
its outer edge) 



group of spots as they transit the apparent face of the S^n. 
Above is a characteristic sun-spot, from a drawing with much 
detail, by Secchi. Also, the opposite illustration indicates 
the regions of greatest spottedness (where the zones are dark- 



The Sun 59 

Other manifestations of this have been recognized 
in tremendous rushes of gaseous matter, moving with 
enormous velocities, to great heights above the solar 
surface. Modern instruments and methods of investi- 
gation have enabled astronomers to trace the action 
and course of these at any time when they are in prog- 

- : but the appearances afterward found to be due 
to them were first perceived on the occurrence of total 
eclipses of the Sun. These phenomena, now known 
to be produced by glowing hydrogen, were long called 

est), and the apparent positions of these zones at the different 
seasons. The Sun's axis is inclined 83 to the plane of the 
Earth's orbit ; and if prolonged northward to the celestial 
sphere, that axis would intersect it near the third-magnitude 




December 6 March 6 June 5 September 5 

APPARENT POSITION OF THE SUN SPOT ZONES AT DIFFERENT 
TIMES OF THE YEAR (PROCTOR) 

{The darker belts show where the spots are more numerous, and indicate 
the apparent direction 0/ spot motions across the disk by solar rotation) 

star 5 Draconis : so that in March the Sun's north pole is 
turned farthest from the Earth; in September it is inclined 
7 toward us. Spectroscopic study of the sun-spots shows that 
their inferior brilliance is due in part to a greater selective 
absorption than obtains in the photosphere generally. Con- 
tinuous and systematic records of the solar spots are now kept 
at Greenwich (in connection with Dehra Dun, India), at Pots- 
dam near Berlin, at Chicago, and elsewhere. Excellent photo- 
graphs of sun-spots and the solar surface have been obtained 
at Potsdam [Himmcl tuid Erde, ii. (1S90) 24; iv , 4S4). This 



60 Stars a?id Telescopes 

red flames, or rose-colored protuberances, attention 
having been first attracted to them during the eclipse 

famous observatory is illustrated on the opposite page; also 
its peculiarly mounted telescope below, with its oblong tube 
and duplicate object-glass, which makes it possible to keep the 
instrument pointed with the greatest accuracy while exposures 
are making with the photographic objective, mounted in a twin 
tube. The advantages of the overhanging pier commend them- 
selves at once to the practical observer. 




THE 12-INCH EQUATORIAL AT POTSDAM 

( The bent pier affords exceptional conven- 
ience of observation) Scale, i inch= 12 feet 

Also at Meudon, Paris, M. Janssev has had extraordinary 
success in photographing the Sun's surface in detail; its gran- 
ulation, sharply defined in his originals, is somewhat blurred 
in the reproduction on page 62. In viewing the Sun with a 
telescope this granulation can be satisfactorily seen with a 
magnifying power of about 400 or 500, under good atmospheric 
conditions. 

While the 42 years' faithful work of Schwabe, as revised by 
Wolf and collated with other and scattering results, gives an 




< 



62 



Stars and Telescopes 



which was total in Switzerland in 1706. 18 It was long 
contested whether they belonged to the Sun or to the 

average sun-spot period of n£ years, there are great irrregu- 
larities : the intervals between maxima have varied from 8 to 
15I years, and between minima from 9 to 14 years. True inter- 
pretation of this indicates with an approach to certainty that 




THE SUN'S SURFACE, OR PHOTOSPHERE (jANSSEN) 

{Showing its granulation and a large circular s/>ot) 

On the same scale the Sun's diameter would be 4 feet, and the Earth like 
this : — 




the cause of the periodicity does not lie in planetary or any 

exterior agency, but that it is seated in the Sun itself. — D. P. T. 

18 Professor Young was the first to photograph a solar 

prominence, in 1870. Of the three prominences here shown, 



The Sun 



6J 



Moon, the dark body ot which concealed the Sun dur- 
ing a total eclipse ; and it was then thought that she 





Great Protuberance 

29th August 1886 
{Height, 150,000 miles) 



Eruptive Protuebkancb 

3d May 1892 
(Trouvelot) 



those of 1S6S and 1S86 were observed during total eclipses 
while that of 1892 was drawn in full 
sun-light, by means of a spectroscope 
adjusted delicately on the edge of the 
Sun, this instrument reducing the sky 
glare, without dispersing very much the 
light of the prominence itself. This 
method has now been in common use 
more than a quarter-century. In Octo- 
ber, 1878, Professor Young observed 
the highest prominence ever recorded, 
which reached an elevation of nearly 
400,000 miles above the Sun's limb. 
Tacchini and Ricco in Italy, Trouve- 
lot and Deslandres of Paris, Maun- 
der and Sidgreaves in England, and 
VON Konkoly and Fenyi in Hungary, 
are the most faithful European obser- 
vers of these wonderful phenomena. 
By means of the spectro-heliograph de- 
vised by Professor Hale of the Uni- 
versity of Chicago, the hindering effects 
of our atmosphere are in considerable 
part evaded. In April, 1S91, he obtained 
the first photograph of the spectrum of 




Solar Prominence,— 
'Great Horn' of 1S68: 

{H eighty 100,000 miles) 



6 4 



Stars and Telescopes 



might be surrounded by an atmosphere which occa- 
sioned these phenomena. But the careful observa- 
tions made during later eclipses (particularly in 
Norway and Sweden in 185 1 and in Spain in i860, 

a prominence ever taken without an eclipse ; and he is enabled 
to secure on a single plate (with a single exposure) not only 
the photosphere and sun-spots, but the chromosphere and pro- 
tuberances. Also the same instrument (which utilizes mono- 
chromatic light, or light of a single color only) has demonstrated 




SUN SPOTS AND THE ZONES OF FACUL^E 
(From a si7igle exposure with Pi-ofessor Hale's spectro-heliograpk) 

that the faculas, which to the eye are ordinarily seen only near 
the Sun's limb, actually extend all the way across its disk, in 
approximately the regions of greatest spot-frequency. By the 
courtesy of Professor Hale, both these results are here illus- 
trated. The bright zones of faculas are related to the promi- 
nences — perhaps identical with them; and they indicate an 
abundance of glowing calcium vapor. His progressive methods 
of solar research will soon afford large accumulations of facu- 
lar observations, from which the laws of their appearance may 




SI N — SPECTROHELIOGRAM BY DESLAXDRES 

{Photographed by the brilliant K line 
attributed to calcium) 



SOLAR CHROMOSPHERE — DEFLANDRES 

( The protuberances rise to a height of about 
30,000 ;;;.. 




SEPT. 3, IO A. M. SEPT. g, 3 P. M. SEPT. IO, II A. M. 

GREAT GROUP OF SPOTS OX THE SUN IN 1S9S 

(From photographs at the Royal Observatory, Greenwich. The Suns diameter on the same 
U is about 9 inches. The largest spot is about 35,000 miles long) 



The Sun 



65 



by Airv, then Astronomer Royal, and by many other 
astronomers) showed clearly, from the way in which 

be filially determined, and their connection with the formation 
of spots and prominences satisfactorily made out. A vast 
advantage has been secured through the recent erection of the 
Maharajah Takhtasingji Observatory at Poona, India, where a 
spectro-heliograph similar to the one at Williams Bay is already 

in operation. Professor Hale's spectro-heliograph is illus- 
trated on page 352. 




the sun's chromosphere (25th July 1892) 

{From a negative obtained with the spertro-heliograph) 



Both spots and prominences have a well-recognized varia- 
tion in heliographic, or solar latitude ; the former has been in- 
vestigated by Dr Spoerer of Potsdam, and the latter by 
M. Ricco of Palermo. Just before the epoch of a minimum 
SAT— 5 



66 



Stars and Telescopes 



they were first covered and then uncovered by the 
Moon, that they were appendages of the Sun. 

(1888, for example), the spots are seen nearest the Sun's equa- 
tor ; coincidently with the minimum, these circum-equatorial 
spots cease, and a series breaks out afresh in high solar lati- 
tudes. Thenceforward to the time of the next minimum, the 
mean latitude of the spots tends to decline continuously, as 
shown in the adjacent diagram. This fluctuation is called ' the 
























/ 


\ 




40 


N^S 


!n 














1 


/ 


-^ 


'*».^ 









Cs. 




' 




! 




s'7 








3<J 










\ 


s s 


f 












~rS> 


























20 




^s 
















/ 




\ 


10° 






X^ 


^ 


—- - 


*.., 












1 


















^« 



































» 



PROMI- 
NENCES 



VARIATIONS IN LATITUDE OF PROTUBERANCES AND SPOTS 

{Prominences according to Ricco, spots according to Sporer) 
(Continuous line, solar latitude north; dotted, south) 

law of zones.' Sporer's careful research farther shows an 
occasional predominance of spots in the Sun's southern hemi- 
sphere not counterbalanced by a corresponding appearance in 
the northern. Also, during the last half of the 17th century 
and the early years of the 18th, there seems to have been a re- 
markable interruption of the ordinary course of the spot cycle,, 
and the law of zones, too, was apparently in abeyance. M. 
Guillaume of Lyons recorded in 1896 two instances of small 
and short-lived spots in solar latitude 44 and 47 . On approach 
of the minimum, there is often a transient outburst of very large 
spots, as in September 1898, well exemplified in the photographs 



The Sun 



"7 



opposite page 64. An unexplained disturbance of the magnetic 
lie, often violent if the spots arc large, takes place coinci- 
dent ly with the appearance Ol spot areas; and there is a 

fairly accurate correspondence between the number of spots 

and the fluctuations of the needle, as exhibited in I) r WOLFER'S 
diagram below. Brilliant auroras, too, are to be expected. 



4 






















3 












































M 








3 














Li 


'"""-—-. 






$ 















92 



"93 



91 



VARIATIONS OF MAGNETIC DECLINATION AND NUMBER OF SPOTS 
{Compared by Dr Wolfer of Zurich) 



As the upper half of the opposite diagram shows, latitude 
variations of prominences follow closely fluctuations of spots, 
although exhibiting greater divergence between the two hemi- 
spheres than the spots do. Professor Young has classified these 
phenomena of the solar limb into eruptive and quiescent promi- 
nences. While the former are metallic and their distribution 
follows nearly the same law of zones as the spots, the latter are 
apparently more cloud-like, and are found in all latitudes, even 
about the solar poles. — D. P. T. 



Sestini, 'Observations of Spots,' Washington Obs., 1S47. 
Carrington, Observations of Spots on the Sun (1853-61) at 
Redhill (London 1863). 

CHIN1 and others, McmSoc. Spettroscopisti Italiani (Palermo 
and Rome, since 1872). 

i.R, Beob. der Sonne nflecken zu Anclavi (Leipzig 1S74). 
Secchi, Le Soldi (2 volumes and atlas), Paris 1875—77. 
Proctor, The Sun: Ruler, Fire, Light I London 1876). 



68 Stars and Telescopes 

NEWCbMB, Popular Astronomy (New York 1877). 
Fievez, Annuaire Obs. Bruxelles, 1879, 2 55- Bibliography. 
Zollner, Wissenschaftliche Abhandlungen, iv. (Leipzig 1881). 
Dewar, McLeod and others, Reports Brit. Assoc. Adv. Sci. 

1881, p. 370 ; 1884, p. 323; 1889, p. 387 ; 1894, p. 201. 
Perry, ' Solar Surface/ Proc. Roy. Institution, xii. (1888), 498. 
Langley, The New Astronomy (Boston 1888). 
Unterweger, ' Lesser Spot-periods,' Denk. kais. Akad. Wis- 

senschaften Wien, lviii. (1891). 
Duner, Recherches sur la Rotation du Soleil (Upsala 1891). 
Fenyi, ' Prominences,' Publ. Haynald Obs. vi. (1892). 
Maunder, ' Sunspots and their Influence,' Knowledge, xv. 

(1892), 128; xxi. (1898), 228. 
Ball, The Story of the Sun (New York 1893). 
V. Oppolzer, E., ' Sunspots,' Astron. and Astro-Phys. xii. (1893), 

4i9» 736. 
Sporer, ' Sonnenflecken,' Publ. Obs. Potsdam, x. (1895). 
Sampson, ' Rotation and Mechanical State,' Mem. Roy. Astr. 

Soc. li. (1895), 123. 
Janssen, Aim. Obs. Astron. Physique Meudon, i. (Paris 1896). 
Young, The Sun — newly revised edition (New York 1896). 
Meyers Konversations-Lexikon,xv\. p. 95 (Leipzig 1897). 
Wolfer, 'Oberflache,' Publ. Stern. Polytech. (Ziirich 1897). 
Very, ' Heliographic Positions,' Astrophys. Jour, vi., vii. 

(1897-98). 

WiLCZYNSKl, Hydrodynamische Untersuchungen mil Anwen- 

dungen anf die Sonnenrotation (Berlin 1898). 
Fontsere y Riba, Sobre la Rotacion del Sol (Barcelona 1898). 

D r Alfred Tuckerman's Index to the Literature of the 
Spectroscope (' Smithsonian Miscellaneous Collections/ No. 658, 
Washington 1888), contains at pp. 88-132 an exceedingly full 
bibliography, conveniently subdivided under sunspots, rotation, 
protuberances, eruptions, chromosphere, corona, solar spec- 
trum in general, solar atmosphere, etc. 



/ 



CHAPTER VII 

MORE ABOUT THE SUN— SOLAR PHYSICS 

' TT is because the secrets of the Sun,' writes Sir Norman 
JL Lockyer, ' include the cipher in which the light messages 
from external Nature in all its vastness are written, that those 
interested in the " new learning," as the chemistry of space 
may certainly be considered, are so anxious to get at and 
possess them.' But even more significant to us are the heat 
radiations of the Sun, because they are determinant in all 
animal and vegetable life, and are the original source of nearly 
every form of terrestrial energy recognized by mankind. 
Through the action of the solar heat-rays the forests of palaeo- 
zoic ages were enabled to wrest carbon from the atmosphere 
and store it in forms afterward converted by Nature's chem- 
istry into peat and coal ; through processes incompletely under- 
stood, the varying forms of vegetable life are empowered to 
conserve, from air and soil, nitrogen and other substances 
suitable for and essential to the life-maintenance of animal 
creatures. Breezes operant in the production of rain and in 
keeping the air from hurtful contamination ; the energy of 
water, in stream and dam and fall ; trade-winds facilitating 
commerce between the continents; oceanic currents modifying 
coast climates (and no less the tornado, the waterspout, the 
typhoon, and other manifestations of natural forces, excepting 
earthquakes, frequently destructive to the works of man), — all 
are traceable primarily to the heating power of the Sun's rays 
acting upon those readily movable substances of which the 
Earth's exterior is in part composed. 

As the Sun shines with inconceivably greater power than 
any terrestrial source, an idea of its total light is difficult to 
convey intelligibly in terms of the ordinary standards of the 



70 Stars and Telescopes 

physicist. Its intrinsic brightness, or amount of light per square 
unit of luminous surface, exceeds the glowing carbon of the 
electric arc light about 3J times, or the glowing lime of the 
calcium light about 150 times. ' Even the darkest part of a sun 
spot outshines the lime light' (Young). Some rude notion of 
the total quantity of light received from the Sun is perhaps 
obtainable on comparison with the average full Moon, whose 
radiance the Sun exceeds 600,000 times. In consequence of 
absorption of the Sun's light by its own atmosphere, the Earth 
receives very much less than it otherwise would; while if the 
absorbing property of that atmosphere were entirely removed, 
the Sun would (according to Professor Langley) shine with 
a color decidedly blue, resembling the electric arc. As a farther 
effect of this absorption, the intrinsic brightness at the edge or 
limb isf that of the centre of the disk (according to Professor 
Pickering) ; and D r Vogel makes the actinic or photo- 
graphic intensity only \ for the same region. While this shad- 
ing off toward the edge is at once apparent to the eye, when 
the entire Sun is projected on a screen, the rapid actinic grada- 
tion is more marked in photographs of the Sun, which strongly 
show the effect of under-exposure near the limb, if the central 
regions of the disk have been rightly timed. 

Kirchhoff of Berlin (whose portrait is given on the fol- 
lowing page) in 1859 formulated the following principles of 
spectrum analysis : (1) Solid and liquid bodies (also gases under 
high pressure) give, when incandescent, a continuous spectrum ; 
(2) Gases under low pressure give a discontinuous but char- 
acteristic bright-line spectrum; (3) When white light passes 
through a gas, this medium absorbs rays of identical wave- 
length with those composing its own bright-line spectrum. 
These principles fully account ior the discontinuous spectrum 
of the Sun, crossed as it is by the multitude of Fraunhofer 
lines. But it must be observed that the relative position of 
these lines will vary with the nature of the spectroscope used : 
with a prism spectroscope the relative dispersion in different 
parts of the spectrum varies with the material of the prism ; 
with a grating spectroscope (in which the dispersion is produced 
by reflection from a gitter, or grating, ruled upon polished 
speculum metal with many thousand lines to the inch), the 
dispersion is wholly independent of the material of the gitter, 
thereby giving the normal solar spectrum. Compared with 
this a prismatic spectrum has the red end unduly compressed, 
and the violet end as unduly expanded. 



Mare about the Sun — Solar Physics 71 

kr rHKRFURD, assisted by Chapman, i uled excellent gratings 
mechanically; but the last degree of Buccess has been attained 
by Professor Rowland of Baltimore, whose ruling engine cov« 

specular surfaces, either plain- or concave, six inches in 
diameter with accurate lines, up to 20,000 to the inch. The 




GUST AVE ROBERT KIRCHHOFF (1824-1887) 



concavity of the gratings vastly simplifies the accessories of 
the spectroscope, for researches in which they arc applicable. 
,reat is the dispersion obtainable that the solar spectrum, 
as photographed by Rowland with one of these gratings and 
enlarged three fold, is about forty feet in length. An illustra- 
tion of his ruling engine is given on p. 72, and its superiority 
consists primarily in the accurate construction and perfect 



72 



Stars and Telescopes 



mounting of the screw, which has 20 threads to the inch, and is 
a solid cylinder of steel, about 15 inches long, and i-J- inches in 
diameter. (Article ' Screw,' Eucydopcedia Britannica, 9th edi- 
tion.) The perfect gratings ruled with this engine are now 
supplied to physicists all over the world. 

By means of a spectroscope properly arranged with suitable 
accessories, the Sun's spectrum has been both delineated and 
photographed alongside of the spectra of numerous terrestrial 
substances. Foremost among recent investigators in this field, 
and in mapping the solar spectrum, are Thollon in France, 
Lockyer and Higgs in England, Thalen in Sweden, Smyth 




professor Rowland's ruling engine 



in Scotland, and in America Rowland, Young, Trowbridge, 
and Hutchins. Their research, together with that of previous 
investigators, principally Kirchhoff and Angstrom, Vogel 
and Fievez, has led to the certain detection of at least 35 ele- 
mental substances in the Sun, among which are : — 

(Al) Aluminium, (Cr) Chromium, (M g ) Magnesium, (Ag) Silver, 
(Ba) Barium, (Co) Cobalt, (Mn) Manganese, (Na) Sodium, 
(Cd) Cadmium, (Cu) Copper, (Ni) Nickel, (Ti) Titanium, 

(Ca) Calcium, (H) Hydrogen, (Sc) Scandium, (V) Vanadium, 
(C) Carbon, (Fe) Iron, (Si) Silicon, (Znj Zinc. 




COMPARATIVE PHOTOGRAPHIC SPECTRA OF THE SUN AND THE 
IRON-COPPER GROUP OF METALS (McCLEAN) 

(Sfark spectra of the metals in air — Metals not alt />urr) 



More about the Sim — Solar Physics 73 

Hydrogen, iron, nickel, titanium, calcium, and manganese are 
most Btrongly marked. Runge's researches in [897 defi- 
nitively established the existence of oxygen in the Sun. Chlo- 
rine and nitrogen, so abundant on the Earth, and gold, nun ury, 

phosphorus, and sulphur, are as yet undiscovered. Also the 
solar spectrum appears to indicate the existence of many metals 
in the Sun not now recognized upon the Earth ; but it must 

be remembered that our globe is known only superficially, and 
there is every reason for believing that the Earth, if heated to 
incandescence, would afford a spectrum very like that of the 
Sun itself. 

On the opposite page is a reproduction from one of M r 
McC LEAN'S large charts of the Comparative Photographic 
tra of the Sun and the Metals (London 1891). The region 
is at the violet end of the spectrum, near the Fraunhofer lines 
H and K, which are due to calcium. The solar spectrum is 
at the extreme top and bottom, with Angstrom's scale, and 
next to it is the spectrum of iron : mark the coincidence of the 
bright lines of the latter with dark lines of the former. In all, 
more than 2,000 coincidences with iron lines have been recog- 
nized. The symbols of other chemical elements are given at 
the left side, opposite their characteristic spectra. The chemi- 
cal spectra of many metallic elements freed from impurities are 
not vet fully known, but these are in the process of thorough 
investigation by Rowland, and Kayser and Runc.e of Han- 
over. On the completion of these researches a farther and more 
searching comparison will be made with the solar spectrum, 
hundreds of the dark lines in which are due to absorption by 
the Earth's atmosphere, and consequently called telluric lines. 
Especial studies of these have been made by MM. Janssen, 
Thollon and Cornu, Becker, and McClean. M r Htggs, 
studying thos? strikingly marked bands in the solar spectrum 
due to absorption by the oxygen in our atmosphere, and known 
as 'great B' and 'great A,' finds that the double lines are in 
rhythmic groups, in harmonious sequence capable of represen- 
tation by a simple geometric construction. Whether the solar 
spectrum is constant in character is not known ; with a view 
to the determination of this question in the future, Professor 
Piazzi Smyth conducted a series of observations for fixing 
the absolute spectrum in the year 1884. 

Regarding the solar spectrum (prismatic) as a band of color 
merely, the maximum intensity of heat-ravs falls just below 
the red (at some distance inferior to the dark Fraunhofer line 



74 Stars and Telescopes 

A); that of light falls in the yellow (between D and E) ; 
and that of chemical or photographic activity, in the violet 
(between G and H) ; but in the normal spectrum, these three 
maxima are brought more closely together, approaching the 
middle of the spectrum which nearly coincides with the yellow 
D lines of sodium. 

Beyond the red in the solar spectrum is a vast region wholly 
invisible to the human eye ; but modern physicists have devised 
methods for mapping it with certainty. Sir John Herschel, 
J. W. Draper, and Becquerel were the pioneers in this re- 
search, the last utilizing various phosphorescent substances 
upon which an intense spectrum had been projected for a long 
time. Direct photographic maps of the infra-red region are 
very difficult, because the actinic intensity is exceedingly feeble ; 
and Abney, by means of collodion plates specially prepared 
with bromide of silver, has made an extended catalogue of the 
invisible dark bands. But Professor Langley has pushed the 
mapping of the infra-red spectrum to an unexpected limit by 
means of the bolometer, a marvellously sensitive energy-meas- 
ure of his own invention. In order to understand in outline 
the operation of the bolometer, or spectro-bolometer, it is neces- 
sary to recall that, as the temperature of a metal rises, it be- 
comes a poorer conductor of electricity ; as it falls, its conduc- 
tivity increases, iron at 300 below centigrade zero being, as 
Professor Dewar has shown, nearly as perfect an electrical 
conductor as copper. The characteristic feature of the bolo- 
meter is a minute strip of platinum leaf, looking much like an 
exceedingly fine hair or a coarse spider web. It is about \ inch 
long, t Jq inch broad, and so thin that a pile of 25,000 strips 
would be only an inch high. This bolometer film, then, having 
been connected into a galvanometer circuit, is placed in the 
solar spectrum formed either by a grating or through the agency 
of rock salt prisms ; and as it is carried along the region of the 
infra-red, parallel to the Fraunhofer lines, the fluctuations of 
the needle may be accurately recorded. 

In this manner he first represented the Sun's invisible heat 
spectrum in an energy-curve ; but his recent application of an 
ingenious automatic method, accessory to the bolometer, has 
enabled him to photograph its indications in a form precisely 
comparable with the normal spectrum. Bolography is the 
name given by Professor Langley to these processes which, 
by the joint use of the bolometer and photography, have auto- 
matically produced a complete chart of the invisible heat spec- 



More about the Sun — Solar Physics 75 



truin equal in length to ten times the entire luminous spectrum 
of the Sun, though indications oi heat extend still farther. Be- 
low, on this page, is an illustration of this extraordinary instru- 
ment, reproduced from a photograph kindly sent me by Pro- 

r LANGLEY. It shows only the bolometer portion of the 
entire apparatus, in its case and with the connections as in 
actual use. The bolometer was built by ( rRUNOW of New York, 
and forms part of the equipment of the astro-physical observa- 
tory of the Smithsonian Institution at Washington. So sensitive 
is this delicate instrument that it is competent to detect a tem- 




BOLOMETER IN WATER-JACKET, WITH CYLINDRIC LENS 

perature fluctuation as minute as the millionth part of a degree 
centigrade. It is proper to add that the researches conducted 
with such an instrument, often appearing remote and meaning- 
less to a layman, are eminently practical in their bearing, as 
thev pertain directly to the way in which the Sun affects the 
Earth, and man in his relations to it, and to the method of dis- 
tribution of solar heat, forming thus, among other things, a 
scientific basis for meteorology. 

At the end of the solar spectrum remote from the red is the 
ultra-violet region, ordinarily invisible ; a portion of which may, 
however, be seen by receiving it upon uranium slass or other 



y6 Stars and Telescopes 

fluorescent substances. Glass being nearly opaque to the short 
wave-lengths of violet and ultra-violet, the optical parts of in- 
struments for this research are made of quartz or calc-spar, or 
the necessary dispersion is obtained by using the diffraction 
grating. The superior intensity of the chemical or actinic rays 
in this region renders photography of especial service ; and 
sensitive films stained with various dyes have been effectively 
employed. The painstaking investigations of Rutherfurd, 
Cornu, H. Draper, Rowland, and Vogel have provided 
splendid maps of the invisible ultra-violet spectrum, exceeding 
many times the length of the visible spectrum. The farther 
region of the ultra-violet is pretty abruptly cut off by the ab- 
sorptive action of our atmosphere. 

The constant of solar heat, first investigated by Herschel 
and Pouillet in 1837-38, was re-determined by Professor 
Langley in 1881. He adopts three calories (small) as the 
solar constant, — which signifies that 'at the Earth's mean 
distance, in the absence of its absorbing atmosphere, the solar 
rays would raise one gram of water three degrees centigrade 
per minute for each normally exposed square centimetre of 
its surface. . . . Expressed in terms of melting ice, it implies 
a solar radiation capable of melting an ice-shell 54.45 metres 
deep annually over the whole surface of the Earth.' Professor 
Langley's Researches o?i Solar Heat and its Absorption by the 
Earth's Atmosphere: A Report of the Mount Whitney Expedi- 
tion, form No. xv of the Professional Papers of the Signal Service 
(Washington 1884). Scheiner (1898) adopts 3.75 calories. 

To express the solar heat in terms of energy : When the Sun 
is overhead, each square metre of the Earth's surface receives 
(deducting for atmospheric absorption) an amount of heat 
equivalent to ij horse-power continuously. In solar engines 
like those of Ertcsson and Mouchot, about | of this is vir- 
tually wasted. Of heat-radiation emitted from the Sun and 
passing along its radius, Professor Frost finds that about \ 
part is absorbed in the solar atmosphere, which, were it re- 
moved, would allow the Earth to receive from the Sun 1.7 
times the present amount. Imagine that hemisphere of our 
globe turned toward the Sun to be covered with horses, ar- 
ranged as closely together as possible, no' horse standing in the 
shadow of any other ; then cover the opposite hemisphere with 
an equal number of horses : the solar energy intercepted by 
the Earth is more than equivalent to the power of all these 
animals exerting themselves to the utmost and continuously. 



More about the Sun — Solar Physics j-j 



It is easy to show thai 'the amount of heal emitted in a 
minute by a square metre of the Sun's surface is about 40,000 
times as that received by a square metre at the Earth, 

that is, over 100,000 horsepower per .square metre acting 
Continuously. 1 . . . (YOUNGJ. It the Sun were solid coal, this 
rale of expenditure would imply its entire combustion in about 
6,000 years. The effective temperature of the Sun's surface is 
difficult to determine, and has been variously evaluated, from 
the enormously high estimates of SECCHI, Ericsson, and 
i m.k, to the more moderate figures of SPOERER and Lank, 
who deduced temperatures 
of So,ooo° to 50,000° Fah- 
renheit. According to Ros- 
11, it is not less than 
18,000° Fahrenheit, an es- 
timate probably not far 
wrong. M. LeChatelier, 
however, in 1S92, found the 
temperature at little short 
of 14.000°, and Wilson and 
Gray, about 12,000°. D r 
Scheiner's recent obser- 
vations upon the peculiar 
behavior of two lines in the 
spectrum of magnesium 
confirm these lower values 
in a remarkable way, ap- 
parently showing that the 
Sun's temperature lies be- 
tween that of the electric 

arc (about 6000°), and that of the electric spark (probably as 
high as 20.000°). 

The maintenance of this stupendous outlay of solar energy 
is explainable on the theory advanced by von Helmholtz 
in 1S56, who calculated that an annual contraction of 250 feet 
in the Sun's diameter will accou r t for its entire radiation in a 
year, — a rate of shrinkage so slow that many centuries must 
elapse before it will become detectable with our best instru 
ments. Accepting this theory. Lord Kelvin estimates that the 
Earth cannot have been receiving the Sun's light and heat 
longer than 20.000.000 years in the past ; and Professor New- 
COMR calculates that in 5,000,000 years the Sun will have con 
tracted to one half its present diameter, and it is unlikely that 




von Helmholtz (1821-1894) 



7 8 Stars and Telescopes 

it can continue to radiate sufficient heat to maintain life of tvpes 
now present on the Earth longer than 10,000,000 years in the 
future. Assuming that solar heat is radiated uniformly in all 
directions, a simple computation shows that all the known 
planets receive almost a two-hundred-millionth part of the 
entire heat given out by the Sun, the Earth's share being about 
i 1 ^ of this. The vast remainder seems to us essentially wasted, 
and its ultimate destination is unknown. 

To epitomize Professor Young's statement of the theory 
of the Sun's constitution, generally accepted : — 

(a) The Sun is made up of concentric layers or shells, its 
main body or nucleus being probably composed of gases, but 
under conditions very unlike any laboratory state with which 
we are acquainted, on account of the intense heat and the 
extreme compression by the enormous force of solar gravity. 
These gases would be denser than water, and viscous, in con- 
sistency possibly resembling tar or pitch. 

(/>) Surrounding the main body of the Sun is a shell of incan- 
descent clouds, formed by condensation of the vapors which 
are exposed to the cold of space, and called the photosphere. 
Telescopic scrutiny shows that the photosphere is composed of 
myriad 'granules,' about 500 miles in diameter, excessively bril- 
liant, and apparently floating in a darker medium. 

(c) The shallow, vapor-laden atmosphere in which the pho- 
tospheric clouds appear to float is called the ' reversing layer/ 
because its selective absorption produces the Fraunhofer lines 
in the solar spectrum. During the India eclipse of 1S98 it was 
shown to be about 700 miles in thickness (pp. 364-65). The 
reversing layer contains a considerable quantity of those va- 
pors which have given rise to the brilliant clouds of the 
photosphere, just as air adjacent to clouds is itself saturated 
with the vapor of water. 

(d) The chromosphere and prominences are permanent gases, 
mainly hydrogen and helium, mingled with the vapors of the 
reversing layer, but rising to far greater elevations. Jets of 
incandescent hydrogen appear to ascend between the photo- 
spheric clouds, much like flames playing over a coal fire. 
Calcium vapor is the most intensely marked, even more so 
than that of iron, which has over 2,000 line-coincidences, while 
calcium has only about 80. In 1895 Professor Ramsay first 
identified helium as an earthy element. 

(e) Still above photosphere and prominences is the corona, 
hitherto observable only during total eclipses, and extending 



More about tlic Sim — Solar Physics 79 

to elevations far greater than any truly solar atmosphere 
sibly could. The characteristic green line of its spectrum, due 

to .1 substance called 'coronium,' is brightest close to the Sun's 

limb, and during the eclipse of 1st January 1889 Jt was traced 
outward by Professor ki I LKR to a distance of 325,000 miles. 
Professor NASIN] of Padua in 1898 announced that, in the 
spectrum of volcanic gases of the Solfatara cli Pozzuoli, he funis 
a line corresponding in position with this coronium line, 1474 I\ 
as it is often called. Coronium may therefore be a terrestrial 
substance, as well as solar. Hut much of the coronal light 
originates in something other than coronium, because of the 
dark lines in its spectrum. These indicate solar light, reflected 
probably from small meteoric particles, possibly the debris of 
comets circulating about the Sun in orbits of their own. Cal- 
cium, hydrogen and helium do not appear in the corona. 

Sir William Huggins and D r Schuster maintain the 
view that the coronal streamers are in part due to electric 
discharges. The corona is a very complex phenomenon, by no 
means fully understood ; and no theory has yet been shown com- 
petent to undergo the ultimate test, — that of predicting the 
general configuration of coronal streamers at future eclipses. 

Among modern solar theories may be mentioned that of 
Schmidt, an optical theory of the solar disk, making the 
Sun wholly gaseous, in fact a planetary nebula; and that of 
D r Brester of Delft, published in 1S92, a theory of the Sun 
characterized by much novelty. Rejecting the hypothesis of 
eruptional translation of solar matter, he conceives the Sun 
to be a relatively tranquil gaseous body, of essentially the same 
elementary composition as our Earth ; and he attempts to 
show, in accordance with well-known properties of matter, 
that the same cause which would keep the mass in repose must 
produce also ' chemical luminescence,' as he terms it. Great 
material eruptions, then, are merely deceptive appearances, 
being simply moving flashes in tranquil, incandescent gases. 

The surface of the Sun (photosphere, spots, faculae, and 
prominences) is now a subject of daily study at many observa- 
tories, particularly at Potsdam, Meudon, Rome, and the Verkes 
Observatory of the University of Chicago; and observations 
are rapidly accumulating, the complete discussion of which 
ought soon to settle many points in the solar theory, now dis- 
puted. But as the Sun's corona is visible only a few hours in 
a century, our knowledge of that object makes haste very slowly. 
and must continue to do so, unless the photographic method 



8o Stars and Telescopes 

of Sir William Huggins (apparently successful in 1883, 
though later not), shall make it possible to study the brighter 
streamers of the corona without an eclipse. Recent results, 
however, are not encouraging. Failing to detect even a trace 
of the corona by its light. Professors Hale and Wadsworth 
have attempted to chart its principal streamers by their heat 
radiations, by means of the bolometer, though as yet without 



For sources of the early and historic papers on the solar 
spectrum by Angstrom, Brewster, the Herschels, father 
and son, Kirchhoff, Mascart, Van der Willigen and 
many others, consult Houzeau and Lancaster, Bibliographic 
Generate, ii. (1882), 800. 
Cornu, * Sur le spectre normal du Soleil,' Ann. de VEcole 

Normale, iii. and ix. (Paris 1874 and 1882). 
Tait, Recent Advances in Physical Science (London 1876). 
Draper, J. W., 'Distribution of Heat in the Spectrum,' in his 

Scientific Memoirs (New York 1878), p. 383. 
Langley, Proc. Am. Assoc. Adv. Science, xxviii. (1879), 51. 
Vogel, H. C, ' Sonnenspectrum/ Pud/. Obs. Potsdam, i. (1879). 
Peirce, ' The Cooling of the Earth and the Sun/ in his Ideality 

in the Physical Sciences (Boston 188 1). 
Haughton, ' Sun-heat and Terrestrial Radiation/ Royal Irish 

Academy (Dublin 1881 and 1886). 
Smyth, Madeira Spectroscopic (Edinburgh 1882). 
Kirchhoff, Gesammelte Abhandlungen (Leipzig 1882). 
Fievez, 'litude du spectre solaire/ Annates de V Observatoire 

Royal, iv. and v. (Brussels 1882 and 1883). 
Siemens, On the Conservation of Solar Energy (London 1883). 
Siemens, ' Solar Temperature/ Proc. Roy. Institution, x. 

(1883), 315. 
Langley, ' Invisible Prismatic Spectrum/ Memoirs Actional 

Acad. Sciences, ii. (1883), 147. 
Sporer, ' Physikalische Beschaffenheit/ Viertel. Astron. Gesell. 

xx. (1885), 243. 
Lockyer, The Che??iistry of the Sun (London 1887). 
Kelvin, 'Sun's Heat/ Proc. Roy. Institution, xii. (1887), I. 
Trowbridge, ' Oxygen in Sun/ Proc. Am. Acad, xxiii. (1888), 1. 
v. Fraunhofer, Gesa?nmelte Schriften (Munich 1888). 
Watts, Index of Spectra (Manchester 1889). 
Becker, ' The Solar Spectrum at Medium and Low Altitudes/ 

Trans. Royal Society Edinburgh, xxxvi. (1890), 99. 



More about the Sun — Solar Physics 8i 

Ma; ' momy t in Chamber 

vol. ii. (Oxford 1890), l)k. viii. 

■7 of the High Sun 

and the Lcno Sun (London 1890). 
THOU W, "^ ni Bsin du spectre solaire,' Annates de 

. with Atlas. 
ICIDT, />/> Strahltnbreckung aufder Sonne 1 Stuttgart 1S91 ). 
Solar Physics, 1 .312. 

ROWLAND, Johns Hopkins University Circular, February 1S91. 
KELVIN, 'On the Age of the Sun's Heat,' and 'On the Sun's 

Heat,' Popular Lectures and Addresses % i. (London 1S91). 
Brester, Theorie du Soleil (Amsterdam 1S92). 
Lk Ch ATELIER, 'Temperature of the Sun,' Astronomy and 

Astrophysics, xi . 11 892 ) . 5 I - . 

PF, Die Sehmidfsche Sonnentheorie (Jena TS93). 
Gore, k Fuel of the Sun,' TheVisible Universe (New York 1893). 
Hig rapine Atlas of the Normal Solar Spectrum, in 3 

series (Liverpool 1S93). 
Hale, 'Corona without Eclipse,' Astron. and Astrophys. xiii. 

(1894), 662. 
Wilson and Gray. ' Temperature of Sun.' Astron. and Astro- 

.. xiii. (1894), 3S2 ; Phil. Trans, clxxxv. (a 1S94), 361. 
Scheiner and Frost, Astronomical Spectroscopy (Boston 1894), 

with bibliographies of numerous papers. 
Langley, *' Infra-red Spectrum,' Nature, li. (1S94), 12; Report 

Brit. Assoc. Adz\ Sci. 1S94, p. 465. 
RAMSAY, ' Helium/ Proc. Roy. Soc. lviii. (1S95), 65, Si. 
Young, 'Helium,' Pop. Sci. Mo. xlviii. (1S96), 339. 
LoCKVER, ' Helium,' Science Progress, v. (1S96), 249. 
vdf.r. ' Helium,' Knowledge, xix. (1S96). 86, 2S4. 
Rowland, Solar Spectrum Wave-lengths (Chicago 1S97). 
Keeler, ' Astrophysics,' Astrophys. Jour. vi. (1S97), 271. 
Clerke, 'Coronium,' The Observatory \ xxi. (1898), 325. 
V el. ' Kirchhoff'schen Spectralapparat,' Sits. Kbn. Prcuss. 

A had. If 'iss. Berlin 1S9S, 141. 
Scheiner. ' Temperature of Sun.' Himmel und Erde, x. (1S9S), 

433; Publ. Astron. Soc. Pacific, x. (1S9S), 167. 

For a nearly complete bibliography of recent literature, con- 
sult Poole's Indexes under Sun, and Spectroscope (page 395 
this booki; Astronomy and Astro-Physics, xi.-xiii. (1S92- 
also The Astrophysical Journal ( i.— viii.) 1S95-1S9S. 

- * T — 6 



CHAPTER VIII 

TOTAL SOLAR ECLIPSES 

T^OTAL eclipses of the Sun, the most impressive 
-■- of natural phenomena, and formerly serviceable 
only to the mathematical astronomer in correcting the 
tables of solar and lunar motions, and in the deter- 
mination of longitudes, are now observed by the astro- 
physicist chiefly, for the knowledge afforded as to the 
Sun's constitution and radiations. 

Nearly. 70 of these phenomena happen every cen- 
tury. In order that an eclipse may be total, the apex 
of the conical lunar shadow must at least reach the 
Earth. But when the Moon is near apogee, its shadow 
does not extend to the Earth, and an eclipse happen- 
ing at that time is of the more frequent type known 
as annular, seven of which take place on the average 
every eight years ; in some regions of our globe the 
Sun may then be seen as a ring of light surrounding 
the Moon's disk. Sir Robert Ball's diagram on the 
opposite page makes clear the relations of Sun, Earth, 
and Moon in eclipses of the various types. 

On the occasion of a total eclipse, the Moon's orbi- 
tal advance, 2,100 miles hourly, causes her narrow 
shadow to trail easterly over the surface of the Earth. 
Total obscuration is visible only within this trail, a 



Total Solar Eclipses 



83 



region which may exceed S,ooo miles in length, but 
whose average breadth near the equator is less than 
100 miles. Obviously, then, a total eclipse at a given 
place must be an exceedingly infrequent occurrence ; 
indeed, every spot on the globe is likely to come 
within the range of the Moon's shadow but once in 
about three and one half centuries. 

While the lunar shadow is sweeping over land and 
sea from west to east, it is to be noted that the axial 




(1) Moon's shadow cut off by earth (total solar eclipse) 

(2) Moon's shadow does not reach earth (annular eclipse) 
13) Moon in earth's shadow (total lunar eclipse) 

(4) Moon's shadow just reaches earth {total solar eclipse in 
middle of path, but annular at both ends) 



rotation of our globe is carrying the observer eastward 
also, 1,040 miles hourly at the equator, so that the 
Moon's shadow as it sweeps past him has a minimum 
speed of 1,060 miles per hour (the difference of the 
two velocities). Swift as this motion is, the lunar 
shadow has repeatedly been seen advancing and re- 
ceding with appalling speed. Total eclipse lasts only 



84 Stars and Telescopes 

while the observer remains within the Moon's shadow. 
It is apparent, then, that the longest total eclipses 
must take place near the equator, because the observer 
located there is transported most rapidly in the same 
general direction as the moving lunar shadow. Also, 
the longest eclipses happen in summer, for the Earth 
is then farther from the Sun, thus making its diameter 
appear smaller, so that our satellite can cover it 
longer. With the Moon near perigee, and other 
necessary and favorable conditions, the calculation 
has been made that it is possible for the Sun to be 
totally obscured nearly eight minutes. Total eclipses 
have every range of duration, from this limit down to 
a single second : but no totality is known to have been 
observed longer than 5 m 36 s (1868, in India), while 
the average duration is about three minutes. 

Eclipses may be approximately predicted by means 
of the Saros, a period of 18 years, \\\ days (or 18 
years, 10^ days, if five leap years have intervened). 
At the end of this cycle another and similar eclipse 
will occur, only 120 of longitude farther west. The 
eclipse of 1896, for example, is a return of the famous 
ones of 1878, i860, and 1842; and there will be 
other repetitions in 19 14 and 1932. When, however, 
three periods have passed, an eclipse may return to 
the same general region on the Earth, but the dis- 
placement in latitude will ordinarily amount to several 
hundred miles; for example, the eclipse of 1842 was 
total in Austria, but its third return in 1896 fell vis- 
ible in Norway. By utilizing the mathematical data 
of the Astronomical Ephemeris, published by the gov- 
ernment three years in advance, a brief computation 
will give the time of every phase of an eclipse, exact 
to a small fraction of a second, for any place on the 



Total Solar Eclipses 85 

Earth where n may be visible. The subject of the 
remarkable recurrence o\ eclipses, and the great pre- 
cision with which they may be predicted, is treated 

more fully in Number 1 of the ' Columbian Knowl- 
edge Series.' 

To select a single salient result from each recent 
eclipse whose observation has important bearing on 
our knowledge of solar physics: 18th August 1868 
(India), when M. JANSSEN, using a high-dispersion 
spectroscope, succeeded for the first time in observ- 
ing the solar prominences after (as well as during) 
the eclipse; 7th August 1869 (Iowa, U. S.), when 
Professor Young at Burlington observed and accu- 
rately identified the green line (1474 on Kirchhoff's 
scale) in the spectrum of the Sun's corona, which 
is regarded as due to the vapor of a solar element 
not yet found on the Earth, and hence called l coro- 
nium ' ; 22nd December 1870 (Spain), when, just 
as totality was coming on, Professor Young observed 
a multitude of the Fraunhofer lines in the Sun's spec- 
trum instantly reversed into bright lines, — a phe- 
nomenon repeatedly confirmed, and which indicates 
the existence of a stratum in the Sun's atmosphere 
known as the ' reversing layer ' ; 12th December 187 1 
(India), when M. Janssen saw Fraunhofer lines super- 
posed upon the faint continuous spectrum of the 
corona; 29th July 1878 (Western United States), 
when Professor Newcomb in Wyoming and Professor 
Langley on Pike's Peak, Colorado, observed a vast 
ecliptic extension of the coronal streamers to a dis- 
tance of eleven millions of miles, east and west of 
the Sun; 17th May 1882 (Egypt), when D r SCHUSTER 
photographed the spectrum of the corona for the first 
time, getting no less than 30 measurable lines ; 6th 



86 Stars and Telescopes 

May 1883 (Caroline Island), when, with a large in- 
crease of knowledge relating to the prominences, the 
coronal structure and its spectrum, the non-existence 
of intramercurian planets was settled to the satisfac- 
tion of most astronomers by MM. Trouvelot and 
Palisa; 29th August 1886 (Grenada), when D r 
Schuster found the maximum actinic intensity in the 
continuous spectrum of the corona displaced consid- 




THE CORONA OF 17TH MAY 1882 
(Wesley, from Schuster's photographs) 

erably toward the red (in comparison with the spec- 
trum of sunlight), proving that the scattering light 
from small particles is feeble; ist January 1889 
(California), when M r Barnard at Bartlett Springs 
and Professor W. H. Pickering at Willows obtained 
exceedingly fine detail photographs of the Sun's 
corona ; 16th x\pril 1893 (Senegal), when M. Deslan- 
dres, by photographs of the coronal spectrum on 




VON OPPOLZER (1S4I-1SS6) 

(Theodor VON Oppolzer, at first a student of medicine, ivas for the last 
thirteen years of his life connected with the European geodetic surrey. 
ti is chief astronomical works are : a comprehensive treatise in two vol- 
umes on the determination of planetary and cometary orbits: and his 
1 Canon der Finstemisse? giving the approximate elements of 5,200 lunar 
and 8,000 solar eclipses, from the earliest times down to A.D. 2163) 




PERRY (1S33-18S9) 

( Perry, director of the Stouyhurst Observatory . 
ducted tzvo government expeditions to transits of I 'err.' 

tlen Island, and issj i n Madagascar i also four ecli/se 
expeditions, in xnd the second total obscuration of \ 

The las* cost him his life. //•• wis a Fellow of the Royal Socie: 
>Pool Astronomical Socu 



Total Solar Eclipses Sy 

both sides of the Sun, found evidence, on comparing 
them, that the corona rotates on its axis bodily with 
the Sun ; 9th August 1S96 (Nova Zembla), when 
M r SHACKLETON verified the existence of the reversing 
layer by photographing its spectrum j 2 2d January 1898 
(India), when M r ^ MAUNDER secured the first fine pho- 
tographs of the outermost streamers of the corona. 

A fact of much significance in solar research, and 
now generally regarded as established, is the periodi- 
cal fluctuation of the streamers of the corona coinci- 
dently, or nearly so, with the eleven year cycle of 
the spots on the Sun. The total eclipse of 1882, on 
the opposite page, shows the type of corona near the 
times of maximum spots, — a corona rather fully de- 
veloped all around the Sun, with an abundance of 
relatively short, bright streamers, often complexly inter- 
laced ; while the eclipse of 1878, in the adjacent 

figure, exhibits the type 
occurring at the sun- 
spot minimum, — a cor- 
ona with uneven radi- 
ance, but with a vast 
extension of its stream- 
ers east and west, and 
beautifully developed in 

The Corona of 2 9 th July 1878 de ]icately curving fila- 

( Harkx ess, /r^w photographs) J ° 

ments around the solar 
poles. The physical cause underlying this cycle of 
the corona is not yet made out ; and the investigation 
of this problem, with a host of others arising in con- 
nection with total eclipses, leads astronomers to an- 
ticipate their occurrence with absorbing interest. 

The total eclipses of the next quarter-century most 
favorable for observation are (map opposite) : — 




Stars and Telescopes 



DATE 


REGIONS OF GENERAL VISIBILITY 


DURATION OF 
TOTALITY 


1900, May 28 


Mexico, United States (from 
New Orleans to Norfolk), 






Spain, and Algeria. 


2 in. 


1 901, May 18 


Sumatra, Borneo, and Celebes. 


6 m. 


1905, August 30 


Labrador, Spain, and Egypt. 


4 m. 


1907, January 14 


Russia, Turkestan, and China. 


2 m. 


1912, October 10 


Colombia and Brazil. 


1 m. 


1914, August 21 


Norway, Sweden, and Russia 


2 m. 


1 91 6, February 3 


N. extremity of S. America. 


2 m. 


1918, June 8 


U. S., from Oregon to Florida. 


2 m. 


1 9 19, May 29 


Brazil, Liberia, and Congo. 


6 m. 


1922, September 21 


Northern Australia. 


6 m. 


1923, September 10 


California to Texas. 


4 m. 


1925, January 24 


Canada and Maine. 


2 m. 


1926, January 14 


Africa, Sumatra, and Borneo. 


4 m. 



The totality-path of the great eclipse of 9th Sep- 
tember 1904, and those of 3rd January 1908 and 
28th April 191 1, unfortunately lie for the most part 
over the unavailable wastes of the Pacific Ocean. No 
total eclipse will be visible in New England or the 
Middle States till 24th January 1925. On 20th June 
1955 occurs the longest eclipse for many centuries, 
totality lasting more than seven minutes in the island 
of Luzon, at or very near Manila. 

A full list of popular articles on eclipses, and the researches 
undertaken by eclipse expeditions to all parts of the world, 
will be found in Poole's Index to Periodical Literature, vol. i. 
(1802-81), pp. 381-2; vol. ii. (1882-86), p. 129; vol. iii. (1887- 
91), p. 127; vol. iv. (1892-96), p. 167. Also, Fletcher's In- 
dex to General Literature (Boston 1893), P- 9°- 
Johnson, Eclipses, Past and Future (London 1874). 
Bessel, Analyse der Finsternisse (Leipzig 1876). 
Ranyard, Menioirs Royal Astronomical Society, xli. (1879). 
Newcomb, On the Recurrence of Solar Eclipses, with Tables of 

Eclipses from B. c. 700 to A. D. 2300 (Washington 1879). 
Huggins, ' Corona,' Proc. Royal Society, xxxix. (1884), 108. 
Hastings, Memoirs National Academy Sciences, ii. (1884), 107. 



Total Solar Eclipses 



89 



v. Oppolzer, T., Canon der Finstermsse (Vienna 1SS7). 

\\ 1 si 1 v. in Chambers' Astronomy (London 1889), '• 3 11 - 

Astronomy (New York 1892). 
Clerks, Hisi ronomy (London 1893). 

Todd, Total. Mclipses of the Sun (Boston 1 894). Bibliography. 
Ginzel, 'Mystische Sonnenfinsternisse,' Himmel und Erde % 

vii. (1895), l6 7- 
LYNN, Remarkable Eclipses (London 1S96). 

xYi.k, Recent and Coming Eclipses (London 1S97). 
KOBOLD, VALENTINER'S Handwbrterbuch der Astronomic, i. 

(Breslau 1897). 

BURRARD, Eclipse 2 2d January 189S, with Charts of Eclipse 

Families (DehraDun 1S98). 

For the literature of current eclipses, consult also the recent 
volumes of Knowledge, The Observatory, Popular Astronomy , 
Journal British Astronomical Association, Publications Astro- 
nomical Society Pacific ; and for technical reports, the Proceed- 
ings and Transactions of the Royal Society. — D. P. T. 




THE LONG CORONAL STREAMERS OF 22D JANUARY 1898 
{From a photograph in India by 3fr* Maunder) 



CHAPTER IX 

THE SOLAR SYSTEM 

'TPHE Earth on which we live is one of a large 
•*• number of bodies circulating in orbits round 
the Sun, and attracted to him by a force called gravi- 
tation, which, constant in itself, acts in such a way 
that its effect diminishes as the square of the dis- 
tance increases. The revolving bodies themselves are 
endued with a similar attracting energy, but much 
smaller than that of the Sun in consequence of the 
much smaller amount of matter which they contain. 
The Sun, the central body of this great system, ra- 
diates light and heat to the whole with an intensity 
diminishing, like the force of gravity, in the same pro- 
portion as the square of the distance increases. 19 

19 Independently of his light and heat, the Sun's supreme 
right to rule his family of planets is at once apparent from his 
superior size (see diagram on page 95), and from his vastly 
greater mass. Relative weights of common things readily give 
a notion sufficiently precise: let the ordinary bronze cent 
represent the weight of the Earth ; Mercury and Mars, then, 
the smallest planets, would, if merged in one, equal an old- 
fashioned silver three-cent piece ; Venus, a silver dime ; Uranus, 
a gold double-eagle and a silver half-dollar (or, what is about 
the same thing in weight, a silver dollar, half dollar, and quarter 
dollar taken together) ; Neptune, two silver dollars ; Saturn, 
eleven silver dollars ; Jupiter, rather more than two pounds 
avoirdupois (37 silver dollars) ; while the Sun, outweighing 
nearly 750 times all the planets and their satellites taken to- 
gether, would somewhat exceed the weight of the long ton. — 
D. P. T 



The Solar System 91 

The bodies known to revolve round the Sun are 
divided into three classes, — planets, comets, and 
meteors. In their orbital revolutions, many of the 





■ . 




^ • - A :^\T1> S'H ANNO* ( 




A qvo pgst urn 1 \^m w wcn>j a 


1 


■ EXIUVtt LlBU?rATi{*v : Difu: 












9 J 'fWW^H^f 


mi 




s $&t&*mm 


2ai3Hti^ : " ^^ElraH ^*m 











TYCHO BRAHE (1546-1601) 

planets are attended by one or more companion bod- 
ies called moons or satellites. Also, some of the 
comets are known to consist of double or multiple 



92 Stars and Telescopes 

portions. But the meteors mostly travel in vast shoals 
together, along orbits similar to those of comets, with 
which they seem to have a connection not yet fully 
understood. 

Kepler, by his laborious research upon the appar- 
ent motions of Mars as obtained from the obser- 




KEPLER (T 571-1630) 

vations of Tycho Brahe, and by extending to the 
other planets by analogy the conclusion derived there- 
from, established three simple laws according to which 
these bodies move in the same general direction 
round the Sun. Kepler's laws are : ( 1 ) The planet- 
ary orbits are ellipses, with the Sun in one focus ; (2) 
the planets move fastest when nearest the Sun, in such 



The Solar System 



93 



a way that the radius vector describes equal areas of 
the ellipse in equal times, as the figure shows ; (3) the 
squares oi the periodic times of the 
planets' revolutions round the Sun 
are proportional to the cubes of their 
mean distances from him. 

The first two of these laws were 
shown by Newton to be necessary 
consequences of the planets being 
attracted by the Sun with a force 
varying inversely as the square of 
the distance ; while the third proves 
that the force of this attraction is the same upon each, 
the actual intensity being, as in the case of each 




TO ILLUSTRATE 

KEPLER'S 2d LAW 

( The six shaded areas 
are all equal) 




SIR ISAAC NEWTON 1643-I727) 

separate planet, inversely proportional to the square 
of the distance from him. 20 

21 The work of both Kepler and Newton relates purely to 
laws of planetary motion, and is in no way whatever concerned 



94 Stars and Telescopes 

The planets vary very much in size, as is apparent 
from the opposite illustration, the largest (Jupiter) 
being more than 1,300 times greater than the Earth, 
while many of the small planets are so minute as to 
be visible only with the aid of powerful telescopes, 
and it is impossible to measure their real sizes. 
These small planets, however, form almost a class of 
themselves. Their mean distances from the Sun are 
all smaller than that of Jupiter, though greater than 
that of Mars, with a single exception ; and their 
faintness arises not so much from their great distance 
as from their really small size. 

All the planets revolve round the Sun in elliptical 
orbits of small eccentricity, not differing greatly from 
circles. 21 These planetary paths are inclined at va- 

with physical causes underlying those laws. Newton himself 
says ; * The cause of gravity is what I do not pretend to know. 
. . . Gravity must be caused by an agent acting constantly ac- 
cording to certain laws, but whether this agent be material or 
immaterial, I have left to the consideration of my readers.' 
Consult Professor Tait's Properties of Matter, pp. 131 -138, 
Clerk Maxwell's article on 'Attraction' (Encyclopedia 
Britannica, 9th edition), and the admirable resume of kinetic 
theories of gravitation by M* W. B. Taylor in the Smithsonian 
Report for 1876. Research upon the mechanism of gravity 
belongs rather to the field of physics than astronomy, and the 
cause of gravitation is yet undiscovered. — D, P, T. 

21 In a subsequent chapter it will be shown how the law of 
gravitation, regnant through untold ages in the remote past, has 
brought about the evolution of the planetary system in its form 
at the present day. But a century and a half ago, it was a mere 
speculation what the future of such a system might be. Gravi- 
tation, that definite and powerful bond, mutual and interacting 
between the Sun and all his planets, maintaining each body in 
its individual orbit, and preserving continual order and har- 
mony, — might it not relax its hold with the lapse of time, leav- 
ing all the planets, the Earth among them, to recede farther and 
farther into the cold of space, thus bringing all organic life to 



The Solar System 



95 



rioua angles to 
the ecliptic or 



Mercury 



an end? Or might 
not the very po- 
tency of that same 
force, through or- 
bital changes then 
known to be going 
on, eventually 
bring down all the 
planetary members 
of the system, with 
their retinues of 
satellites, upon 
the Sun in terrible 
cataclasm ? I n- 
deed, Euler, who 
made the first suc- 
cessful attempt to 
develop fully the 
significant results 
from the law of 
gravitation, had 
written a letter 
from Berlin in 
I749t0\VETSTEIN, 
stating his conclu- 
sion that the 
Earth's motion 
had been sensibly 
accelerated in the 
three centuries 
previous. He nat- 
urally accounted 
for this by the hy- 
pothesis of a sub- 
tile resisting me- 
dium, causing all 
the planets to 
travel round the 
Sun in slowly 



Venus 

Earth and 
Moon 

Mars and two 
satellites 



Several 
hundred 
small planets 



Jupiter 
and five 
satellites 



Saturn 
and eight 
satellites 



Uranus and 

four 

satellites 



Neptune 
and one 
satellite 



9 6 



Stars and Telescopes 



plane of the Earth's orbit, and the courses of a few 
small planets are considerably more inclined to the 

involving spirals, with the rapidity of their motion augmented 
at every revolution by increasing nearness to the Sun, Mani- 
festly, then, the solar system could not last forever in its pres- 
ent state. The eminent French astronomers, La Grange 
(whose portrait is opposite) and La Place (page 246), attacked 
this great problem of stability of the planetary system ; and 
by the application of mathematical methods and expedients, 
newly invented, solved it. The path in which each planet 
travels has certain geometrical characteristics ; its form, its 
size, and its position relatively to the stars in space. Tech- 
nically these are termed the elements of the orbit, and every 
orbit has six such elements. La Grange and La Place, pro- 
ceeding on the hypothesis 
that all the planets were rigid 
bodies, proved that no inter- 
action of gravity among them 
could ever alter the average 
size of their orbits ; and that 
the values of the other ele- 
ments could only oscillate 
harmlessly within certain 
narrow limits which their 
researches were competent 
to define. So long, then, as 
the inherent force of gravity 
remains constant, the solar 
system, in itself considered 
and independently of ex- 
terior influences, possesses 
all the elements necessary to 
absolute stability in stzcnla 
sceculorum. The farther researches of Poisson and Le Ver- 
rier in France, of Schubert in Germany, and of Stockwell 
in America, have contributed greatly to our accurate knowledge 
of these important terms. 

The eccentricity of the Earth's orbit, then, could not go 
on increasing indefinitely in the future ; so that our globe is 
forever insured against the possibility of retreating at one sea- 
son so far from the central luminary that all the waters of the 




euler (1707-1783) 



The Solar System 97 

ecliptic than the orbits of the large planets are. Also, 

the orbital eccentricities of the small planets present a 
wider range. 




LA GRANGE (1736-1S13) 

Earth would freeze ; nor at the opposite season could it ever 
approach so near the Sun that all forms of life would become 
extinct by reason of the excessive heat. It is the path of our 
own planet in which interest chiefly centres : its eccentricity, 
already given in Chapter VI as 0.01677, mav var y between the 
limits 0.0047 ar *d 0.0747, according to Le Verrif.r. It is di- 
minishing at the present time ; that is, our yearly path round 
the Sun is now approximating more and more nearly to the cir- 
cular form, and its nearest approach will take place about 
24,000 years hence ; after which the orbit will again grow more 
and more elliptical. The relatively minute fluctuations of an 
orbit are termed secular variations; and thev mav be crudely 
represented by holding a flexible and nearly circular hoop 
between the hands, now and then compressing it slightly, also 
wobbling it a little, at the same time slowly moving the arms 
one about the other. 

Lv Place's mathematical investigations in his Micanique 
s ft T — 7 



98 Stars and Telescopes 

But, whether large or small, the planetary bodies 
are all alike in partaking of the same easterly motion 
in their orbits round the Sun. Comets (at least those 
which are permanent members of the solar system) 
also move about the Sun in elliptic orbits ; but their 
inclination and eccentricity are generally much greater 
than those of the planetary orbits, and many which 
travel in very elongated ellipses move in the reverse 
direction from that of all the planets. Of the meteors, 
those moving in regular orbits pursue paths like those 
of many comets, swarms of them travelling in ellipses 
nearly identical with known cometary orbits. Indeed, 
it would seem not unlikely that many comets are com- 
posed of clusters of meteors loosely kept near together 
by the feeble bond of attraction of the separate parti- 
cles, similar discrete bodies being scattered along the 
whole or a part of the orbit, but more thickly congre- 
gated in some portions than in others. 

The large planets at present known are eight in 
number : Mercury, Venus, the Earth, Mars, Jupiter, 
Saturn, Uranus, and Neptune. The mean distances 
of Mercury and Venus from the Sun, in proportion to 
the Earth's, are 0.387 and 0.723, respectively; and 
the mean distance of Mars from the Sun is 1.524, of ' 

Celeste also led him to the discovery of the invariable plane of 
the solar system, which passes through its centre of gravity, 
and is determined by the dynamical principle that the sum of 
the products of all the planetary masses by the projection of 
the areas described by their radii vectores, in any given time, is 
a maximum quantity. Relatively to the ecliptic, or ordinary 
plane of reference, the invariable plane is defined as follows : — 

Longitude of its ascending node, 106 14' 6" 
Its inclination to the ecliptic, 1 35 19, 

according to Stockwell, one of the latest investigators who 
have calculated its position. — D. P. T. 



The Solar System 99 

Jupiter 5.203, of Saturn 9.539, of Uranus 19.183, and 
of Neptune 30.055 times that of the Earth.* 9 

Recalling that the distance of our globe from the Sun is 
93,000,000 miles, these numbers readily give the approximate 
ccs in miles of all the large planets from the central 
luminary. There has been devised no better illustration of 
relative distances, magnitudes, and motions in the solar system 
than the following, from Sir John Herschel's Outlines of 
Astronomy : 'Choose any well leveled field or bowling-green. 
On it place a globe, two feet in diameter ; this will represent 
the Sun ; Mercury will be represented by a grain of mustard 
seed, on the circumference of a circle 164 feet in diameter for 
its orbit ; Venus a pea. on a circle of 2S4 feet in diameter; the 
Earth also a pea, on a circle of 430 feet ; Mars a rather large 
pin's head, on a circle of 654 feet ; the asteroids, grains of sand, 
in orbits of from 1000 to 1200 feet; Jupiter a moderate-sized 
orange, in a circle nearly half a mile across ; Saturn a small 
orange, on a circle of four-fifths of a mile; Uranus a full 
sized cherry or small plum, upon the circumference of a circle 
more than a mile and a half; and Neptune a good sized plum, 
on a circle about two miles and a half in diameter. As to 
getting correct notions on this subject by drawing circles on 
paper, or, still worse, from the very childish toys called 
orreries, it is out of the question. To imitate the motions of 
the planets, in the above-mentioned 
orbits, Mercury must describe its 
own diameter in 41 seconds ; Venus, 
in 4 m 14 9 ; the Earth, in 7 minutes ; 
Mars, in 4 m 4S 8 ; j upiter, in 2 b 56 m ; 
Saturn, in 3 h i3 m ; Uranus, in 2 h 
io"; and Neptune, in 3 h 30™. ' 

Among the great astronomers 
who, at the beginning of the present I 
century, turned their attention to 
the important problem of deter- 
mining a planet's motion from ob- 
servation, Gauss is pre-eminent, 

and his finished work is embodied gauss (i777 -I S55) 

in his Theoria Motus Corporum 

CaUstium (1S09), translated by Admiral Davis (1S57). The 
large planets, with the exception of Uranus and Neptune, have 




ioo Stars and Telescopes 

It has often been surmised that there is a planet 
(possibly several planets) nearer the Sun than Mer- 

now been accurately observed so long a time, and the elements 
of their motion are so thoroughly well ascertained, that it is 
possible to predict their future positions with a precision which 
is satisfactory for most purposes. This is done through the 
instrumentality of Tables of their motion, which extend ordinarily 
a half century in advance of their date, and are capable of farther 
extension indefinitely. From such tables is prepared each year, 
by a tedious and complex arithmetical process, The Nautical 
Almanac and Astronomical Ephemeris, which gives the data 
required by navigators in conducting ships from port to port, and 
by astronomers in carrying on the operations of observatories. 
Some of these data are the accurate positions of all the planets 
among the fixed stars ; and the degree of their precision de- 
pends upon (i) the perfection of the mathematical theory of 
their motion and (2) the accuracy with which the planets have 
been observed, chiefly during the past two centuries. It is at 
the great observatories maintained by the principal govern- 
ments that such researches are systematically kept up: at 
Greenwich, founded 1675 (already shown on page 39) ; Ber- 
lin, founded in 1700; Paris, founded in 1668 (on page 141); 
Washington, founded in 1842 (page 101, an illustration of the 
new Observatory, completed in 1893), an d elsewhere. The ex- 
pense of maintenance of each of these establishments averages 
about $50,000 annually. Sir George Airy, seventh Astrono- 
mer Royal at Greenwich (from 1835 to 1881), whose portrait 
is on page 102, was the most eminent of the modern astronomers 
who have devoted themselves to planetary observation. Since 
the time of his early predecessor, Bradley, in the middle of 
the* 18th century, observations of the planets had been accumu- 
lating in unavailable form, and Airy undertook and completed 
the prodigious task of calculating, or reducing them, as the 
technical expression is. This finished product of the observa- 
tory formed the basis of Le Verrier's tables of all the princi- 
pal planets of the solar system, completed in 1877, and published 
in the Annales de V Obsei-vatoire Imperial de Paris, Memotres. 
An entirely new system of tables has now for many years 
been in progress of construction under the immediate direc- 
tion of Professor Newcomb, who gives in the Introduction to 
volume i, Astronomical Papers of the American Ephemeris 



102 Stars and Telescopes 

cury ; but such objects must be very small, and none 
have yet been certainly discovered. The number of 
small planets now known is almost 450 ; many new 
ones are discovered every year, and there probably 
are more than 1000 in all. Whether there are planets 
more distant than Neptune it is impossible at present 




SIR GEORGE AIRY (180I-1892) 

(Washington 1882), a brief and lucid review of a century's 
progress in planetary tables. Also in his Fle?ne?zts of the Four 
Inner Planets and the Fundamental Constants of Astronouiy 
(Washington 1895), ne presents a general summary. — D.P. T. 



The Solar System 103 

to say ; but such bodies would not be visible without 
the aid o( a powerful telescope.- 3 

28 Professor Todd in 1S77 (from unexplained deviations of 
Uranus), and Professor FORBES in 1880 (from the aphelion 
distances of a family of comets thought to have been captured 
by planetary bodies far exterior to the present boundary of the 
solar system), derived two independent positions for the trans- 
neptunian planet which are in surprisingly good agreement; 
but, although the suspected region among the stars has been 
carefully searched, both optically and photographically, this 
planet is not yet visualized. — D. P. T. 



Airy, Gravitation (London 1834). 

Hansen, Allgemeine Uebersicht des Sonnejisy stems, in Schu- 
macher's * Jahrbuch,' xv. (1837). 

Hind, The Solar System (London and New York 1852). 

MAEDLER, Das Planetensystem der Sonne (Leipzig 1854). 

Breen, The Planetary Worlds (London 1854). 

Kirkwood and Chase, Papers on planetary mechanics and 
harmonies in A?n. Jour. Science, Proc. Am. Phil. Society, 
Jour. Fraftk. Institute^ and Proc. Am. Assoc. Adv. Science. 

Le Verrier, American Journal of Science, xxxii. (1861), 222. 

Klein, Das Sonnensystem (Brunswick 187 1). 

Kaiser, Measures of all the planets with double-image microm- 
eter, A/iualeu der Steruzuarte in Leide/i, iii. (Hague 1872). 

Stockwell, ' Secular Variations of Orb ts of Principal Plan- 
ets/ SviitJisonian Contributions to Knoivlcdge, xviii. (1873). 

Alexander, ' Harmonies of the Solar System,' Smithsonian 
Contributions to Knozuledge, xxi. (1875). 

Gladstone, 'Chemical Constituents of the Solar System,' 
Ph ilosoph ical Magazine, iv. (1877), 379. 

Ledger, The Sun: Planets and Satellites (London 1882). 

Scheiner, Frost, Astronoitiical Spectroscopy (Boston 1S94). 

Boys, * Newtonian Constant of Gravitation,' Nature, 1. (1894), 
330, 366, 400; Phil. Trans, clxxxvi. (A 1895), x - 

Hill, ' Progress of Mecanique Celeste,' Observatory, xix. (1S96). 

PoiNCARE, 'Stability of Solar System,' Nature,\v\\\. ( 189S), 183. 

Skeliger, 4 Law of Gravitation,' Pop. Astron. v. ( 1S9S), 474, 544. 



CHAPTER X 



THE PLANETS 



HP HE large planets of the solar system are classified 
-■" as inferior planets (Mercury and Venus), and 
superior planets (Mars, Jupiter, Saturn, Uranus, and 
Neptune). As seen with a telescope, the inferior 
planets pass through all the phases of the Moon. The 
phases of Venus were first noticed by Galileo in 1610. 
The orbits of Mercury and Venus lying wholly 

within that of the Earth, 
these planets can never 
come into apparent op- 
position to the Sun as 
seen from the Earth. 
But either body may 
come from time to time 
into line or conjunction 
with the Sun, called in- 
ferior conjunction when 
it is between Sun and 
Earth, and superior con- 
junction when beyond 
the Sun. If one of them 
when in inferior conjunction is near the node of its 
orbit, where it crosses the plane of the Earth's, the 
planet will be seen to pass like a round black spot 
across the Sun, and this phenomenon is called a 




gassendi ( 1 592-1655) 




The Planets 105 

transit. The first time Mercury was ever seen on the 
Sun's disk was by GaSSENDI at Paris, 7th November 
1 63 1. The transit of 7th November 1677 was well 
observed by Halley at Saint Helena. Dates of re- 
cent transits are 9th May 
1 89 1, and 10th November 
iS 94 . i4 

Mercury can be seen with 
the naked eye only when 
near greatest elongation from 
the Sun (which averages 
about 2 3 and never exceeds 
28 ), a little before sunrise 
or after sunset, as the case 
may be. He revolves round MERCURY (^erscHiAPAREix,) 

, _, . _, „ , Earth's diameter on the same scale = 

the Sun in 88 days at a 3 inches 

mean distance ot 36 millions 

of miles ; but, as the eccentricity of his orbit is con- 
siderable, his actual distance from the Sun varies 
between 28^ and 43^ millions. Mercury is too 

24 As the Earth passes Mercury's descending node about 7th 
May, and the ascending node about 9th November, transits are 
possible near these dates only. Also this planet's path being 
very eccentric, and at its least distance from the Sun near the 
time of its passing the November node, there are about twice 
as many transits in November as in May, if long periods of time 
are considered. And while the greatest length of a May transit 
is 7 h 50™, Mercury's swifter motion near perihelion reduces the 
maximum duration of a November transit to 5 h 24™. About 13 
transits of Mercury take place every century, the intervals being 
either 3^, 7, 9J, or 13 years. A period of 46 years (exact to 
about J day) rarely fails of a return of any given transit. Pro- 
fessor Nf.wcomb's researches on the motion of the Moon lead- 
ing him to suspect that the Earth's rotation on its axis might 
be variable, he has investigated this question by means of the 
independent time-measure furnished by Mercury's motion round 



io6 



Stars and Telescopes 



near the Sun to allow us to see anything very dis- 
tinctly on his surface. His diameter is about 3,000 
miles. As shown on the preceding page, markings on 
the surface of Mercury have been carefully observed 
during several years by Professor Schiaparelli of 
Milan, indicating that the planet has a rotation on 
its axis equal in duration to its revolution round the 
Sun. Mercury's mass is about one tenth that of the 
Earth, and his density is therefore much greater than 
that of our planet. 25 

the Sun; but his critical discussion of 21 transits of the planet 
observed from 1677 to 1881, afforded no conclusive evidence 
of change in the length of the day. (Astronomical Papers of 
the American Ephemeris, i. 465.) Following are the transits 
during the half century, 1875-1925: — 



Date 


Eastern Standard 

Time of 

Mid-transit 


Duration 
of Transit 


Position of Transit-path 
on the Sun's Disk 


1878 May 6 


2 h jm p M 


7 h 28 m 


Considerably north 
of centre. 


1881 Nov. 7 


7 57 p - M - 


5 17 


Slightly south of 
centre. 


1891 May 9 


9 24 P. M. 


4 47 


Near south limb. 


1894 Nov. 10 


I 34 P.M. 


5 13 


Slightly north of 
centre. 


1907 Nov. 14 


7 7 A.M. 


3 21 


Near north limb. 


1914 Nov. 7 


7 5 A.M. 


4 4 


Near south limb. 


1924 May 7 


8 34 P. M. 


7 47 


Very nearly central 



Transits of Mercury are chiefly useful in physical observa- 
tions of the planet, its distance from the Earth being generally 
too great to allow its throwing any light on the problem of the 
Sun's distance, although the May transits, when the planet 
comes within 50,000,000 miles of the Earth, might advanta- 
geously be photographed for this purpose. — D. P. T. 

25 Recalling Professor Darwin's theory of tidal evolution 
(vide Chapter XVI) it is important to observe that the near 



The Planets 



107 




THE HEMISPHERES OF VENUS 
(NIESTEN AND stuyvaert) 



Venus moves in an orbit more nearly circular than 
that of any other of the principal planets, and her dis- 
tance from the Sun never varies much from 6 7 \ mil- 
lions of miles. She revolves round him in 225 days. 
The inclination of 
her orbit to the 
Earth's is greater 
than that of any 
other except Mer- 
cury's. The great- 
est elongation of 
Venus from the Sun 
amounts to about 
45 , so that she 

may sometimes be seen for a very considerable part 
of the night, before sunrise or after sunset. In very 
ancient times she was called, when seen in the morn- 
ing, Phosphorus, and when seen in the evening, 
Hesperus. 

The transit of Mercury in 1677 led Halley to sug- 
gest the observation of transits of Venus as the best 
means of obtaining the distance of the Sun. Venus 
had already been seen on the Sun by Horrox and 

proximity of Mercury to the Sun, together with the small 
surface-gravity of the planet, render it a priori extremely prob- 
able that the periods of axial rotation and orbital revolution are 
identical. Also, observations by M r Denning in 1882, and in 
1S92 by Professor W. H. Pickering at Arequipa, Peru, appear 
to confirm this view. Although Mercury seems to have no 
atmosphere, or one of extreme rarity, the markings upon its 
surface are exceedingly faint. Professor Schiaparelli finds 
the axis of Mercury perpendicular to the path of its motion 
round the Sun. One side of the planet, then, must be con- 
stantly in full sunlight, the other remaining in total darkness ; 
but on account of the large libration, the Sun is forever hidden 
from only ♦ of the planet's surface. — D. P. T. 



108 Stars a?id Telescopes 

Crabtree in 1639; but no other transit would take 
place until 1 7 6 1 . The transit of that year, as well as 
the following transit in 1 769, was extensively observed, 
and so have been those of 1874 and 1882. The next 
pair will occur in the years 2004 and 2012. 26 





1st December 5th December 

VENUS NEAR INFERIOR CONJUNC- 
TION IN 1890 (BARNARD) VENUS, 20TH FEBRUARY 

189 1 (trouvelot) 



The diameter of Venus is 7,700 miles, not quite 
equal to that of the Earth. Her mass, likewise smaller 
than that of our planet, indicates that her density also 
must be somewhat smaller. There is doubtless a 
very considerable atmosphere surrounding Venus, and 
loaded with clouds so dense as to render it very diffi- 
cult to observe her surface distinctly, and to deter- 

26 As Venus revolves almost exactly 13 times round the Sun 
while the Earth is completing eight revolutions, the general law 
of recurrence of transits of Venus is quite simple. In cen- 
turies adjacent to the present, transits occur in pairs, eight 
years elapsing between the two transits of each pair, and the 
intervals between the midway points of the pairs being alter- 
nately 113^ and 129^ years. Usually, then, one pair will fall 
in each calendar century, and a June pair in one century will 
be followed by a December pair in the next, transits being pos- 
sible only in the earlier days of these months, when the Earth 
is passing the planet's nodes. The 19th century pair having 
taken place only recently, no transit of Venus will occur in the 
20th century, and the pair belonging to the 21st will happen 











M.ich iX March 22 March 28 

THE DISK OF MERCURY IN 1897 (LOWELL) 

(Dur , .1/'" PbRCIVAL LOWELL at Flagstaff, Arizona, and in 

Mexico* modi a fine scries of observatio>is of Mercury* S disk with his 24- 
iuch Clark telescope. His first result was a confirmation of Schiapar- 
elli's conclusion, that the planet's axial and orbital periods are the same. 
Three of M>' Lowell's dra:viugs are given above, and a combhiation of 
all of them etuibled him to draw a complicated map of the plane? s mark- 
ings, a characteristic feature of which is a close cross-hatching, best 
explained by either cracks or corrugations as a result of the plane? s 
cooling. His results were i7idependently confirmed by Miss Leonard and 
M r Drew. Probably Mercury' 's small mass is incapable of retaining an 
atmosphere, absence of which is corroborated by the observations) 




October 23 October 25 October 25 

THE DISK OF VENUS IN 1896 (LOWELL) 

{In August-October 1896, Mr Lowell, assisted by Mr Drew, observed also 
the disk of Venus, and their work is confirmatory of Schiaparelli's, as 
to coincidence of axial and orbital periods. Three of M* Lowe ll's draw- 
ings are here given, and his chart of the planet's surface subsequently 
constructed was independently confirmed by M* Douglass in 1898, using 
every precaution to prevent deception. The spoke-like markings always 
Tttaintain the same relation to tJie terminator, and the plane f s axis is 
perpendicular to its orbit plane. Notwithstanding an evident atmosphere 
of dazzling lustre, W Lowell finds the markings invariably visible ; 
that is, tJie atmosphere is cloudless. Probably the hemisphere of Venus 
always turtied from the Sun is exceedingly cold, and the supposition 
of a polar Jiemisphere would explain t/ie ' phosphorescence,' so-called, re- 
peatedly observed on the perpetually unillumiued regions of the disk. 
Precedent to incorporation with the body of established astronomical 
fact, these interesting observations of tJie inferior planets yet await full 
confirmation elsew/iere. The Flagstaff observers insist, and reasonably, 
that an atmosphere of great tranquillity, not a telescope of great power, 
is the prime requisite for visualizing delicate planetary features) 



The Planets 



109 



mine with certainty the time of her axial rota- 
tion. It was, indeed, thought that periodical changes 
had been seen indicating a rotation in about 
2j h : 1 m ; but such conclusion is now regarded by 
astronomers as very doubtful. As Professor New- 
COMB says, 'The circumstance that the deduced times 
of rotation in the cases both of Mercury and Venus 
differ so little from that of the Earth is somewhat 

early in that century. The last pair of transits of Venus and 
the next to occur are as follows : — 



Date — Eastern Standard Time 


Duration of 
Transit 


Limb of the 
Sun 


1874 December 8, n h P. M. 
1SS2 December 6, noon. 
2004 June 8, 4 a. M. 
2012 June 5, 8 P. M. 


3 h 33 m 

5 37 

6 2 
6 20 


North. 
South. 
South. 
North. 



Of any December pair of transits (ascending node), the 
path of the earlier one always lies across the Sun's northern 
limb; and of the later one, across the southern limb. For any 
pair of June transits (descending node), the circumstances are 
reversed, the earlier one always crossing the Sun's south limb, 
and the later one the north limb. The shortest transit of Venus 
ever observed was that of 1874. Several centuries hence, when 
Venus passes centrally across the Sun, the maximum length of 
transit, equal to 7 h 58 111 , will be reached. As the inferior planets 
are always retrograding, or moving westerly, at the time of 
transit, it is important to notice that ingress always take place 
on the Sun's east limb, just the opposite of the solar eclipse, 
which always begins on the west side of the Sun. 

Many observers in the 17th and 18th centuries thought they 
had discovered a satellite of Venus ; but M. Stroobant has 
satisfactorily disposed of nearly all these observations by other 
hypotheses. As none of the great telescopes of the present 
day reveal any such body, the existence of a satellite of Venus 
is extremely improbable. — D. P. T. 



no Stars and Telescopes 

suspicious, because if the appearance were due to any 
optical illusion, or imperfection of the telescope, it 
might repeat itself several days in succession, and 
thus give rise to the belief that the time of rotation 
was nearly one day.' Professor Schiaparelli's re- 
cent observations would seem to show that Venus as 
well as Mercury rotates in the same time in which she 
revolves round the Sun ; but M. Perrotin thinks 
that the rotation of Venus, though very slow, is prob- 
ably not quite so slow as this. 27 

27 Among the famous astronomers who observed Venus in 
the 17th and 18th centuries were Cassini at Paris, Bianchini 
at Rome, ScHROETERat Lilienthal, and Sir Wiliam Herschel 
in England. The mountains supposed to have been seen by 
Schroeter were not visible to Herschel, nor can they be 
seen at the present day. Near the middle of the 19th century, 
Maedler and De Vico made careful studies of the planet, and 
many astronomers have in recent years turned their attention 
to Venus, but with slender avail. Among them M r Denning 
made several fine sketches in the spring of 1881 ; and MM. 
Niesten and Stuyvaert, observing at Brussels 1881-1890, 
saw a great deal of detail, as the illustration on page 107 shows, 
embodying all their drawings into a chart of both hemispheres 
of Venus. In the same year M. Trouvelot published a series 
of observations made partly at Paris and partly at Cambridge, 
U. S., and extending through fifteen years. A pair of narrow 
white markings at the opposite edges of the disk were usually 
visible when properly illuminated, and they are thought to be 
snow caps at the planet's poles. Occasionally large gray spots 
could be seen covering equatorial regions. The terminator, 
sometimes seen as a wavy line, rather than straight or slightly 
elliptical, has by its roughness in certain parts assisted in 
affording an idea of elevations and depressions on Venus, and 
in estimating the time of rotation. While this is to be regarded 
as well determined, it is a little less than 24 hours, according 
to M. Trouvelot. On page 108 is one of his sketches of the 
planet, near the time of greatest elongation. The little double 
drawing adjacent to it represents Venus as seen at times when 
she is very nearly between the Earth and Sun ; her dense at- 




The Plaints 1 1 i 

i much smaller planet than the Earth, his 

in diameter being only 4,230 miles; but the ellip- 
ticity of his figure is greater, the difference between 
his polar and equa- 
torial diameters being 
about a hundredth 
part of the latter. 
The mass of Mars 
is about one ninth 
that of the Earth, 
and his density, less 
than that of Venus, 
is only about three 
fifths that of our globe. 
Mars revolves round M ars, ist august 1892 (flammabion) 
the Sun in 68 7 days, 
at the mean distance of 141^ million miles. 

The disk of this planet is well seen with our tele- 
scopes at the favorable oppositions, and many maps 
have been drawn of the surface, which exhibits in 
many respects a striking analogy to that of the Earth. 
It differs, however, in this, that on Mars the propor- 
tion covered, or thought to be covered, by sea is con- 
siderably smaller than that which is apparently dry 

mosphere appearing like a very slender sickle or crescent of 
silvery light, the horns of which M r Barnard saw, 5th December, 
1S90, nearly meeting together. A similar observation had been 
made under more favorable circumstances by Maedler in 1S49, 
and in December 1866, by Lyman, both of whom saw the delicate 
atmospheric ring completely encircling the planet, and made 
measures of it which enabled them to calculate that the hori- 
zontal refraction in the atmosphere of Venus is 54'. As the 
corresponding quantity for the Earth is only 35', the greater 
density of the atmosphere surrounding Venus is readily 
inferred. — D. P. T. 



112 Stars and Telescopes 

land. The duration of the axial rotation of Mars is 
a 24 h 37 111 2 2 s . 7, a constant now very accurately known. 
The axis is inclined to the orbit at an angle of about 
6$°, somewhat less than in the case of the Earth ; so 
that the inclination of his equator to the plane of 
orbital motion is greater by 3^° than it is on our 
planet. Mars is surrounded by an atmosphere, prob- 
ably of no great density. 




MARS AND THE APPARENT ORBITS OF ITS SATELLITES 

In August 1877 Professor Hall discovered that 
this planet is attended by two satellites, to which he 
afterward gave the names Phobos and Deimos. 28 The 

28 The illustration on the preceding page represents Mars 
as drawn by M. Flammarion at Juvisy when the planet was 
35,800,000 miles from the Earth, or very near its minimum dis- 
tance. The minute satellites of Mars, so long in being discov- 
ered, but so easy to see with large telescopes once their existence 
became certain, have been glimpsed with instruments of very 
moderate capacity, one of the smallest being the 7J inch Clark 
glass of the Amherst College Observatory, with which, near the 
opposition of 1892, I saw both satellites without great difficulty. 
Their apparent orbits are indicated in the above illustration. 
At the favorable oppositions they are remarkably easy objects 
in the Lick telescope ; indeed, Professor Keeler in 1890 ob- 
tained a few successful observations of eclipses of Phobos by 
the shadow of the planet. With the exception of the minute 



The Planets 



"3 



inner of these (Phobos) is the brighter, and likely 
somewhat the larger of the two ; but neither of them 
probably exceeds ten miles in diameter. The period 
of the inner satellite round Mars is 7 h 39™ i5 s .i ; that 
of the outer, 30 11 1 7™ 54 s .o. The distance of Phobos 
from the centre of Mars is only about 6,000 miles, so 
that its distance from the nearest point of the planet's 
surface must be less than 4,000 miles. Deimos is 
about two and a half times as far from Mars as 
Phobos, its distance from 
the planet's centre being 
approximately 15,000 
miles. 

s Hundreds of small plan- 
ets are now known to re- 
volve round the Sun in 
elliptic paths lying be- 
tween Mars and Jupiter. 
The smallest orbit is only 
a very little less than that 
of Mars, and the largest 
is not much smaller than 
the orbit of Jupiter. While ^thra (132) when at peri- 
helion is actually nearer the Sun than Mars is at aphe- 
lion, no small planet yet discovered ever recedes so 
far from the sun as the perihelion distance of Jupiter. 
(433) Eros (p. 408) has the smallest mean distance 

particles composing the dusky ring of Saturn, the inner satellite 
of Mars is the only secondary body in the solar system known 
to revolve round its primary in less time than the planet takes 
to turn round once on its axis, a seemingly strange relation 
which is easily accounted for by the secular action of tidal 
friction. So great interest attaches to Mars that I have thrown 
the fuller additions on this planet into a separate chapter, fol- 
lowing the present one. — D. P. T. 
s &T — 8 



m 



C H. F. PETERS (1813-189O) 



114 Stars and Telescopes 

(1.457 in terms of the Earth's mean distance) ; while 
that of Thule (279) is the greatest, amounting to 4.247 
on the same scale. The first four small planets were 
discovered in the early years of the 19th century (the 
first, Ceres, on the 1st January 1801), and these are 
probably the largest; but it is not likely that the 
diameter of any one of them exceeds 300 miles. 
After the discovery of the fourth (Vesta), in 1807, 
no more were found until 1845, wnen Astraea was de- 
tected. 29 Since then discovery has been nearly con- 

29 Peters (portrait on the preceding page), the most suc- 
cessful American discoverer of small planets, calculated the 
diameters of 40 of these bodies found by him, the mean of 
which is 43 miles. M r Barnard in 1894 measured the largest 
with the Lick telescope as follows: Ceres, 485 miles; Pallas, 
304 miles ; Vesta, 243 miles. M r Roszel estimates the united 
mass of the first 311 small planets at 3-2V0 tnat °f tne Earth. 
In a general way the group of these bodies ranges through 
f of the broad interval between Mars and Jupiter, or about 280 
million miles. Their orbits, by no means concentric, also ex- 
hibit wide divergence from a median plane. While the orbital 
inclinations of six small planets exceed 25 , the mean inclina- 
tion to the ecliptic for the entire group is only 8°, not much 
more than that of Mercury. In general, orbits greatly inclined 
are also very eccentric. The periodic times of the small plan- 
ets vary between 1.76 and 8.75 years. Regarding their cosmic 
origin, the explosion hypothesis of Olbers was long ago aban- 
doned, and it is now commonly considered that their discrete 
existence is sufficiently explained by the proximity of the ex- 
cessive mass of Jupiter, whose perturbative influence in this 
region prevented the concentration of primordial planetary 
material into a single body. Kirkwood in 1866 directed atten- 
tion to the fact that in those portions of the small planet zone 
where a simple relation of commensurability exists between 
the appropriate period of revolution and the periodic time of 
Jupiter, gaps are found, similar to those which separate the 
rings of Saturn. Minute intercomparison of their orbital ele- 
ments reveals numerous instances of a near identity of paths 
about the Sun, or an apparent grouping, sometimes only in 



The Planets \ \ 5 

tinuous ; and of late years a large number have been 
found by photography. The number at present known 
is about 450. 

pairs, but several times in families, one of which includes ir 
members. Some of the outer members of the group suggest a 
transition between small planets and periodic comets J the path 
of Andromache (179), for example, being very like the orbit of 
TSMPEL'S comet. Minute and distant as these bodies are, the 
careful observations of M* PARKHURST have established the 
fact of a phase (peculiar to each minor planet), which cannot 
be neglected in comparisons of brightness at different times. 
Studies of the small planet group have been made by Monck, 
Tisseram), NlESTEN, and others, among them Kirkwood, 
whose researches are embodied in his monograph entitled The 
Asteroids or Minor Planets (Philadelphia 1S88). For complete 
data respecting the orbits of these bodies, consult the most 
recent issue *of the Berliner Astronomisches Jahrbuch. The 
simple facts of interest connected with their discovery are 
given in a table at the end of this book. 

The striking advantage of photography is shown in the ra- 
pidity and thoroughness with which the sky is now searched 
for new objects of this character; for example, M. Charlois 
of Nice, the most successful of all discoverers, using a portrait 
lens of 6 inches diameter, and 32 inches focus, obtains every 
star to the 13th magnitude, on plates including more than io° 
square on a side; that is, an area covered by 400 full moons 
arranged in a square, 20 on a side, with their disks just touch- 
ing. Each plate is exposed 2\ hours, and its critical examina- 
tion requires an equal amount of time; so that in five hours, a 
given region of the sky can be more thoroughly searched than 
in 90 hours by the old-fashioned method, at the eyepiece of a 
telescope. New discoveries of small planets are now double- 
lettered, provisionally, until observed at least five times ; then 
a permanent number is assigned in the regular list. The first 
small planet found in 1894 is lettered A Q, and most of the 
recent discoveries are still without names. There is a growing 
recognition of the significance of the small planet group in the 
cosmogony ; and it is hoped that an international agreement 
may soon be reached, looking toward the more even distri- 
bution of the vast labor of the calculations which the rapidly 
increasing discoveries of these bodies now entail upon the pa- 
tience of Germany almost unaided. — D. P. T. 



n6 Stars and Telescopes 

Exterior to the small planets are four bodies very 
much larger than the four planets interior to this 
group. Of these, the nearest to the Sun is the. largest 
planet of all, Jupiter, often called the ' giant planet.' 
His bulk is 1,309 times as great as that of our globe, 
his mean diameter being 86,500 miles. But his mass 
being only 316 times that of the Earth (or xoW that 
of the Sun), his density is apparently less than a quar- 
ter that of our planet. He revolves round the Sun at 
a mean distance of 483^ millions of miles in a period 
amounting to nearly twelve (11.86) years. 30 

30 Jupiter, always during its visibility a magnificent planet 
among the stars, was first mentioned by Ptolemy, who re- 
corded its near approach to the star 5 Cancri, 3d September, 
B.C. 240. About ten times as bright as a Lyrae and Capella, 
many modern observers, knowing just where to look, have 
found it visible in full daylight. Bright as Jupiter is, at times 
almost sufficient to cast a shadow, it would require 6,500 such 
stars to equal the lustre of the full Moon. D r Lohse, during 
a conjunction of Mars and Jupiter in 1883, found from his pho- 
tographs of these planets that the intensity of the actinic or 
chemical rays reflected from Jupiter was 24 times stronger than 
that of Mars, and that the two hemispheres of Jupiter were by 
no means alike, the light from the southern hemisphere being 
twice as effective as that from the northern. Not until 1630, 
nearly a quarter-century after the invention of the telescope, 
were its conspicuous belts discovered by Zucchi, at Rome. 
The phase effect on Jupiter, though slight, is not difficult to 
detect when the planet is near quadrature and can be seen at a 
high altitude in twilight. 

This giant planet, the most satisfactory of all celestial objects 
for scrutiny with a small telescope, has already been depicted 
on pages 30 and 95, as seen with instruments of moderate 
capacity. As the edge or limb of the planet is approached, 
not only the colors of the markings but their definiteness fades 
out completely. Area for area, Jupiter receives but 2V tne 
heat from the Sun that the earth does, and its own intensely 
heated condition must in large measure account for the exces- 
sive cloud. Professor Newcomb's value of the mass of Jupiter 



The Planets 117 

The great elliptieity of Jupiter's figure attracts 
attention the moment the planet is seen with a mod- 
erately large telescope. This polar compression (or 
fraction representing the difference between polar and 
equatorial diameters divided by the latter) amounts 
to T \ T , according to the best measures (that of the 
Earth is only t>] J; v). The planet is surrounded by 
a thick atmosphere, in which are dense masses of 
cloud. The belts and spots on the apparent disk are 
interesting objects of study; and a large red spot, 
first noticed in 1878, has attracted very special atten- 
tion during the last few years, undergoing remarkable 
changes in brightness, while retaining the same form 
and size. Observations of the spots have given the 
time of Jupiter's axial rotation with some approach to 
accuracy. Being about 9 h 56™, it is less than that of 
any other planet whose rotation is known. The axis 
being nearly perpendicular to the plane of the orbit, 
the equator makes but a very small angle with the 
latter. 31 



adopted in his investigations of planetary motion, is yoTYTS 
that of the Sun. M r Barnard's recent measures with the Lick 
telescope give for the equatorial diameter of the planet 90,190, 
and for the polar, 84,570 miles. These correspond to apparent 
diameters 38". 52 and 36 // .u, respectively, for a distance of 
Jupiter from the Earth equal to 5.20 times that of the Earth 
from the Sun. — D. P. T. 

31 Jupiter's rotation on his axis, first determined by Cassini 
about 230 years ago, presents many points of resemblance to 
that of the Sun. The equatorial regions revolve most rapidly, 
and bright spots on that part of the planet have quite uniformly 
given a rotation in about 9 h 50-£ m . Receding from the equator, 
either north or south, the atmospheric markings revolve in 
longer periods, but the exact relation to Jovian latitude is not 
yet established. Following are a few of the better recent de- 
terminations for regions other than equatorial: — 



1 1 8 Stars and Telescopes 

As soon as telescopes were directed to Jupiter, it 
was seen that he had four attendant moons or satel- 



1880. Schmidt . * . 9 55 34.4 

1885. Hough 9 55 37.4 

1886. Marth 9 55 4°-6 

1887. Williams 9 55 36.5 

1898. Denning ..... 9 55 37.7 

The last depends upon 29 years' observation of the great 
red spot; and should this object eventually prove to be actually 
permanent part of the body of the planet, M r Denning's value 
must be very near the truth. So rapid is this rotation, and so 
great the size of Jupiter, that a point on its equator travels 
nearly eight miles a second. 

These differing periods of rotation have suggested a theory, 
now accepted by many astronomers, that entire zones of the 
Jovian atmosphere, as well as indi- 
vidual spots in it, may differ in ro- 
tation period, the dense envelope 
perhaps drifting in sections quite 
independent of each other. The 
great white equatorial belt is at 
times nearly free from markings of 
any kind, and it usually exceeds 
all other features in brilliance, the 
markings upon it being often ex- 
jupiter, 20th july i88 9 (keeler) ceedingly faint, as shown in the 
, accompanying illustration. Small 

AS SEEN WITH THE 36-INCH ^ J °. 

lick TELEscorE spots of an intenser white, and 

{Earth on the same scale, the size *bout 2 5 00 to 35OO miles across, 

of a pm-head) are sometimes seen upon it, and 

they are presumably at the highest 
level of all the cloud formations in Jupiter's atmosphere. 
These bright spots going through a complete rotation in 5J 
minutes less than that of the great red spot, must pass it at a 
speed exceeding 250 miles per hour; and in six or seven weeks 
they make a complete revolution round the planet, relatively 
to that well-known marking. This vast whirling cloud mass, 
banding the planet's equator, is about 20,000 miles in breadth, 
and has been termed the 'hurricane girdle.' Also, occasional 
small white spots appear on the light strip south of the southern 




The Planets 119 

lites. Their discovery is generally attributed to 
Galileo, who noticed them first on 7th January 1610, 

equatorial belt, which is usually more active than the northern 
one, its detailed configuration often changing rapidly. The 
principal belts are variable in color and intensity of tint, their 
hue being sometimes brownish, coppery, or purple. Usually 
the darkest and most permanent regions of these great belts 
are their edges adjacent to the planet's equator. Lesser changes 
in form and intensity are frequent, but long observation has es- 
tablished the essential permanence of their general outlines. 

The belts on Jupiter's tropics are not uniform in color in the 
two hemispheres, the southern one having a strong reddish tint, 
and the northern one shading into blue and gray. They seem 
to be regions relatively little disturbed, and have no connection 
with the rapidly whirling equatorial belt, except through the 
oblique streamers, often seen trailing over them, as Professor 
Keeler's drawing shows. The extensive polar regions adja- 
cent to both poles of the planet beyond these median belts are 
sometimes seen banded nearly to the pole, and the prevailing 
tint of the northern region is bluish. 

It is not to be inferred that the very great differences of il- 
lumination in the apparent disk of Jupiter indicate anything 
more than fleeting cloud-configurations. But while this atmo- 
spheric envelope may be said to resemble that encircling our 
own globe, it is by no means identical with it ; in fact its metallic 
vapors render it more nearly like a solar atmosphere than a 
terrestrial one. The intense heat of the great globe, its activity 
and its rapid rotation, all tend to complicate the atmospheric 
movements and configurations, about which there is much re- 
maining unexplained, and which must continue so until the 
variable markings have been more critically and persistently 
studied. Members of the British Astronomical Association 
have banded together for detailed research upon this planet's 
surface, having made as many as 200 drawings in a single 
year ; and Mr Stanley Williams's painstaking investigation 
of an excellent series of photographs of Jupiter is effecting 
substantial advances. 

Careful studies of Jupiter's spectrum by D r Huggins in 
England, and D r Vogel in Germany, have revealed a dark 
band in the red, which may indicate some substance in the 
planet's atmosphere not present in our own. The fluctuations 



120 Stars and Telescopes 

and gave in his Sidereus Nuncius an account of his 
subsequent observations, proving them to be satel- 

of long period in Jupiter's atmosphere are matched by detail 
variations of intensity in the lines of its spectrum. Whether or 
not Jupiter may be slightly self-luminous, is, according to D r 
Scheiner, a question upon which the spectroscope furnishes 
but little evidence. 

The great red spot, excellently shown in Professor Keeler's 
drawing on p. 118, was probably first recorded in recent times 
by Gledhill and Mayer in 1S69. Ten years later many 
observers had noticed it, and there are indications that Cassini 
at Paris observed it in 1685. The gigantic size of Jupiter may 
be imagined from the magnitude of this object, the superficial 
area of the elliptical spot alone exceeding the surface area 
of the whole Earth. About the middle of 1883 it nearly disap- 
peared ; was so faint the year after as to be very difficult to 
observe, and in 1885 a white cloud apparently covered its cen- 
tral portions, making it appear like a flattened ring. In this 
year and the one following, the intensity of the spot was slightly 
recovered ; but onward from that time it grew gradually less 
and less easy to see until 1891, when there was again a partial 
return to its former visibility. So that fluctuations of this 
familiar object are now well recognized. To Professor Wilson 
in October 1S91, and M r Williams at the end of 1892, it ap- 
peared quite pale in the middle regions, as if a bright elliptic 
ring. Also it seemed to be very diffuse, as if covered in part 
with a veil of dense mist. If this object is periodic, it must now 
be near another minimum, as M r Barnard reports it as very 
faint in the Lick telescope in 1894-95. Often this spot has been 
observed to exercise a strikingly repellent effect upon cloud- 
markings near it. The great red spot, and its variations of 
form and visibility, have for years been studied, not only by 
many foreign astronomers, but by Professor Hough with the 
18J inch Chicago telescope, whose measures place this strange 
marking at a considerable south latitude, and make its length 
about 30,000 miles, and its width 8000 miles. Many astrono- 
mers think that this persistent object is simply a vast fissure in 
the outer atmospheric envelope of Jupiter, through which at 
times are seen the dense red vapors of interior strata, if not the 
actual surface of the planet ; but its slow drift in longitude, and 
its slight shift in latitude are unwelcome obstacles to this 



The Planets 



121 



lites. Simon Marius (or rather Mayr) claimed to 
have discovered them a few weeks before Galileo ; but 
this was contested, and at any rate he did not pub- 
lish his observations until later. Mayr's proposed 
names for the satellites are not much used, lest per- 
haps such acceptance should seem to imply recogni- 
tion of his claim to the first discovery. Galileo named 
them jointly the Medicean stars, in honor of the 
Grand Duke of Tuscany, and individually after mem- 
bers of his family ; but these designations have been 
dropped by general consent, as all were discovered at 
the same time, and were called the First, Second, 
Third, and Fourth Satellite respectively, reckoning 
according to their distance from Jupiter outward, and 
this nomenclature has been found quite sufficient. 

THE SATELLITES OF JUPITER 



Number 

of 
Satellite 


Name 


Distance 
fromCentre 
of Jupiter 


Synodic Period 
or Mean Interval 
between Eclipses 


Diameter 


Mass in 
Terms of 
Jupiter 


I 


Io 


Miles 
261,000 


d h m s 
1 18 28 35.945 


Miles 
2,500 


0.0000169 


II 


Europa 


415,000 


3 '3 17 53-735 


2,100 


0.0000232 


III 


Ganymede 


664,000 


7 3 59 35-854 


3-55o 


0-0000884 


IV 


Callisto 


1,167,000 


16 18 5 6.92S 


2,960 


0.0000425 



A fifth satellite, probably not exceeding 100 miles 
in diameter, was discovered by M r Barnard at the 



theory. Proctor maintained that the real globe of Jupiter lies 
far within the globe we see and measure, and that the atmos- 
pheric envelope is perhaps 10,000 miles in depth. Professor 
Hough thinks that all the observed phenomena can be best 
accounted for by assuming that Jupiter is still in a gaseous 
condition. — D.P, T. 



122 Stars and Telescopes 

Lick Observatory, 9th September 1892. Its distance 
from the centre of Jupiter is only about 1 12,000 miles, 
and it revolves around him in u h 57 111 22. s 7. 32 



THE LICK OBSERVATORY ON MOUNT HAMILTON, CALIFORNIA 

{Elevation of the summit plateau, 4200 feet above sea level) 

{Professor James E. Keeler, Director) 

Next beyond Jupiter, and next in size, is Saturn, the 
equatorial diameter of which is about 73,000 miles, 

32 The possession of one of the practical handbooks named 
on page 396 will add greatly to the interest of the young ob- 
server ; and the Nautical Almanac will be requisite in identify- 
ing and following the ever changing configurations of the four 
bright satellites, as they undergo their frequent eclipses by 
dropping into the planet's shadow, and pass alternately behind 
the planet and in front of it, their little shadows dotting the 
brilliant disk like a transit of Mercury or Venus in miniature. 
The opposite drawing represents such a phenomenon ; to an eve 




The Planets 123 

so that its bulk is rather more than half that of the 
giant planet, and would contain the Earth's about 

placed anywhere within the black spot, a total eclipse of the 
Sun takes place. It is no unusual thing for two such solar 
eclipses to happen upon Jupiter at the 
same time (though of course not at the 
same place), caused by two different 
moons. During a Jovian year a specta- 
tor on Jupiter who could transport him- 
self anywhere at will on that planet 
might observe S,Soo eclipses of Sun and 
moons. 

From La Place's relation between Jupiter, i8th Febru- 
the mean motions and longitudes of the ary 1874 (Knobel) 
three inner satellites, it is impossible 

that all of them can ever be eclipsed at the same time, but 
it sometimes happens that while two of these satellites are 
eclipsed the fourth is also undergoing eclipse; and the remain- 
ing satellite, being of necessity on that side of the planet oppo- 
site its shadow, may be projected upon the disk of Jupiter, 
where it will usually be invisible. Also this interesting phe- 
nomenon may happen from numerous other conditions of 
configuration. One of the longest recorded instances when 
this great planet was seemingly devoid of its wonted retinue of 
satellites was that observed by the writer at Amherst College 
Observatory, 21st March 1874, when no satellites could be 
seen for nearly two hours. 

Markings upon the satellites of Jupiter were repeatedly seen 
by the earlier observers, Dawes, Lassell, and Secchi. the first 
of whom gives drawings of what he saw, in the Monthly Notices 
Royal Astronomical Society, xx. (i860), p. 246; and in 1897 these 
bodies were intently scrutinized with the fine 24-inch Clark 
refractor in Arizona, belonging to M r Lowell. From observa- 
tions of their surfaces M r Douglass reports the disks of satel- 
lites I and III striped with series of narrow bands, which he 
has charted, and which have enabled him to ascertain the true 
period of rotation of these satellites on their axes. He finds 
the period of I to be I2 h 24 m .o, and confirms Professor W. H. 
Pickering's earlier observations (p. 125), assigning an equal- 
ity between axial and revolution periods to both III and IV. 
Also the little disks have been carefully observed with the 



124 



Stars and Telescopes 



760 times. But its density is not much more than 
half that of Jupiter, and the mass of the latter is equal 



great Lick telescope, two drawings made with which are here 
shown. M r Barnard has made interesting studies of the first 

satellite which, having an 
equatorial region relatively 
bright, is sometimes seen very 
much elongate, when pro- 
jected on a dark belt of Jupi- 
ter ; while on a bright belt, 
the satellite's central region 
coalescing with it, the two 
relatively dark polar regions 
of the satellite may give the 
deceptive appearance of a 
double body. Professor W. H. Pickering at Arequipa, Peru, 
in 1892, and at the Lowell Observatory in Arizona, 1894, has 




JUPITER S THIRD SATELLITE 

As drawn independently by Campbell 
{left) and Schaeberle {right), 23d 
October 1891 




EYE-END OF THE LICK TELESCOPE 

(showing the 6-inch finder , and mechanical accessories for handling the 

telescope) 



The Planets 



125 



to three or four times that of Saturn. Indeed, the 
mass of Jupiter is more than double that of all the 



seen surface detail upon all 
the satellites except the sec- 
ond. His observations in- 
dicate that the equator of 
the first satellite is appre- 
ciably elliptical, not circular, 
and that it revolves on its 
axis in a retrograde direc- 
tion. Satellite I exhibits 
many striking peculiarities 
of form not easy to account 
for. II is more difficult to 
observe, and its axial period 
is not known. The corre- 
sponding periods of III 
and IV are the same in 
duration as their periods of 
revolution round Jupiter, 
therefore resembling the re- 
lation of our Moon to the 
Earth. A white spot was 
several times seen near the 
north pole of IV. 

M r Barnard's new fifth 
satellite was discovered 
with the telescope here 
shown, the chief instrument 
of the great observatory 
founded by James Lick in 
1875 (P- T . 22 )- It: has not yet 
been seen with any telescope 
of less than 183 inches ap- 
erture ; and the eclipses of 
this minute body, whose 
successful observation 
would have so great sig- 
nificance in exact astrono- 
my, appear to be beyond the optical reach of all telescopes at 
present in existence. M. Tisserand, applying the principles 




THE LICK TELESCOPE 

with which Jupiter* s $th satellite was 

discovered 

{Lens 1 ft. i7i diameter. Ttibe 57 ft. long) 



126 Stars and Telescopes 

other planets put together, while his volume is about 
one and a half times as great as the aggregate of all 
the rest. The compression of the figure of Saturn is 
the greatest of all the planets, and amounts to as 
much as one tenth. Saturn revolves round the Sun in 
29^ years, at a mean distance from him equal to 
886 millions of miles. 

Belts are seen on Saturn similar to those on Jupiter, 
but they are much fainter on account of the greater 
distance from both Sun and Earth. Nevertheless, by 
the aid of white spots in the equatorial belts in 1894, 
M r Williams found the axial period of that region to 
be io h i2 m 35*8. The axis of Saturn makes an angle 
of about 6 2 with the plane of its orbit, so that the 
planet's equator is inclined about 28 to that plane. 33 



of celestial mechanics to the motion of this satellite, finds that 
its short period, combined with the great equatorial protuber- 
ance of Jupiter, produces a swift motion of the major axis of 
the satellite's orbit, so rapid, indeed, that the orbit makes a 
complete revolution in about five months. — D. P. T. 

33 Saturn, always shining as a dull reddish star of about the 
first magnitude, is the farthest planet from the sun of those 
which have been known from the remotest antiquity. Its 
light as a whole is subject to some variation, owing to our 
position relatively to the Saturnian rings : when the Earth is 
near their plane, Saturn appears to be 2J times less bright than 
when our globe is at the greatest elevation of 26 above or 
below the plane of the rings ; therefore, its brightness will 
slowly increase until 1899, and then as slowly diminish till 
1907. The mass of Saturn is -gsVo that of the Sun, as deter- 
mined by Professor A. Hall, jun r , from observations with the 
Yale heliometer in 1885-7. So slight is the density of the planet 
that it would float in water; probably, as surmised in the case 
of Jupiter, the real Saturn is very much smaller than the ball 
we measure, and surrounded by a gaseous envelope many hun- 
dred miles in depth. The ball of Saturn has sometimes been 
observed to assume an abnormal figure, very much flattened at 




SATURN, WITH ITS RINGS IN VARIOUS PHASES 

f Scale , about 70,000 miles to the inch. Neglecting unimportant technical details, these 
are the appearances of the planet, as viewed with an inverting telescope ; in 1891 and 
1907 (lower fg?ire), in 1895 anc ^ I 9° 2 {middle), and in 1899 {upper figure). From 1892 
to 1907 the tiortheru face of the ring is turned toward the Earth ; and the southern 
face is similarly turned from 1907 to 192 1) 



128 Stars and Telescopes 

There are now known to be eight satellites revolv- 
ing round Saturn. Owing to the confusion which 
arose from the order of discovery being different from 
that of distance from the planet, it became necessary 
to give them names, and those proposed by Sir John 
Herschel have been generally accepted. Of their 
actual sizes, only very rough estimates are possible : 
Titan, the largest, is probably about 3,500 miles in 
diameter, Japetus 2,000, and Rhea 1,500; while each 

the poles, and very much bulged out at the four regions about 
midway between poles and equator, giving it roughly the 
shape of a square with rounded corners. This phenomenon, 
first observed by Sir William Herschel in 1805, and several 
times verified by other astronomers, is known as the 'square- 
shouldered aspect of Saturn ; ' but no satisfactory explanation 
of so strange an anomaly has yet been advanced. 

Careful studies of this planet were made by the Bonds at 
Harvard College Observatory, 1848-51, and by Lassell with 
his twenty-foot reflector at Malta in 1852-53; also by Dawes 
in 1855-56, M. Trouvelot in 1872-75, M r Ranyard in 1883, 
and M. Terby of Louvain in 1887. In more recent years, 
several astronomers at the Lick Observatory, among them 
Professor Keeler and M r Barnard, have employed the 
36-inch telescope in observing this unique planet to the greatest 
advantage, and the fine illustrations on page 127 embody sub- 
stantially everything that can be certainly seen under the best 
conditions. Excellent photographs of Saturn showing clearly 
the belts on the planet and its system of rings have been taken 
by Professor Pickering, the brothers Henry, and others. 
The absorption at the edge of the ball, and the differing bright- 
ness of the rings are well brought out; but, as in the case of 
Mars and Jupiter, the photographs hitherto taken do not show 
the minute details secured by close optical scrutiny of these 
bodies directly with the telescope. No phase of Saturn's ball 
is perceptible, even in the largest instruments. The spectrum 
of the ball is difficult to delineate ; but according to Huggins, 
Secchi, Vogel, and Janssen, the first of whom observed it 
in 1864 an d photographed it in 1889, its lines are practically 
identical with those of Jupiter. — D. P. T. 



The Planets 



129 



THE SATELLITES OF SATURN 









Distance 






Name of 


Name of 


Date of 


from 


Sidereal Period 


Satellite 


Discoverer 


Discovery 


Centre of 
Saturn 


of Revolution 








Miles 


d 


h m s 


Mimas 


W. Herschel 


17 Sept. 1789 


117,000 


O 


22 37 5-7 


Enceladus 


\Y. Herschel 28 Aug. 1789 


157,000 


.1 


8 53 6.9 


Tethys 


J. D. Cassini ! 2i Mar. 1684 


186,000 


I 


21 18 25.6 


Dione 


J. D. Cassini 21 Mar. 1684 


238,000 


2 


17 4i 9-3. 


Rhea 


J. D. Cassini 123 Dec. 1672 


332,000 


4 


12 25 11. 6 


Titan 


C. Huygens 25 Mar. 1655 


771,000 


[ 5 


22 41 23.2 


Hyperion 


W. C/Bond 16 Sept. 1848 


934,000 


21 


6 39 27.0 


Japetus 


J. D. Cassini 25 Oct. 167 1 


2,22C,000 


79 


7 54 171 



of the four interior satellites, besides Hyperion, is 
probably less than 1,000 miles in diameter. 34 



34 The visibility of the Saturnian satellites corresponds to 
the order of their discovery, a very small telescope sufficing to 
show Titan, also Japetus in the western portion of its orbit, 
where it is 4J times as bright as on the other side of the planet. 
Mimas and Hyperion, the satellites last discovered, are always 
difficult objects, even in very large telescopes. The orbits of 
the rive inner satellites are sensibly circular. At the great 
Russian observatory shown on the following page, D r Her- 
mann Struve, son of the late Director of the Observatory, 
D r Otto Struve, has for many years been prosecuting a 
thorough investigation of the Saturnian system, both mathe- 
matically and by means of observations with the 30-inch 
telescope (page 133). He has brought to light a sensible 
acceleration in the motion of Mimas, the innermost satellite, 
during the last few years. Also its orbit is inclined i° 26' to 
the equator of Saturn; and as its nodes have a motion of 
about i° each day, the orbit returns to its previous position at 
the end of every year. D r Struve's researches farther have 
verified from observation the remarkable connection existing 
between the orbits and motions of Mimas and Tethys, and of 
Enceladus and Dione, previously developed from theory by 
Professor Newcomb. Also the latter has investigated the 
motion of Hyperion, the seventh satellite, the perisaturnium 
s&t — 9 




Q 

P 
P 

o 
< 

6 
Q 



P 



o |. 
•J <q 



The Planets 131 

Saturn is unique among the planets in the posses- 
sion of a ring, or rather system of concentric rings, 
surrounding it within the orbits of all its satellites.. 
When Galileo first, saw Saturn with a telescope, he 
was astonished to see what he thought a small body 
adhering to it on each side, which afterward disap- 
peared, recalling to his mind the old myth about 
Saturn devouring his own children. Huygens was 
the first to explain the real nature of the appendage 
and its varying appearance according to the posi- 
tion of Saturn with regard to Sun and Earths This 
he did in 1656, at the end of a pamphlet announc- 
ing his discovery of the satellite Titan the year 
before, which contains a Latin anagram, afterward 



of whose orbit has an extraordinary regression in a period of 
about 1 8 years. The perisaturnium is that point in the path 
of a satellite of Saturn which is nearest the planet ; and as 
these points ordinarily partake of an advance motion, Hyperion 
has afforded a novelty in celestial mechanics, to which the 
ordinary mathematical methods were found entirely inapplica- 
ble. The cause of this anomaly was traced to the perturbative 
action of Hyperion's massive inner neighbor, Titan, three 
times the motion of which nearly equals four times that of 
Hyperion. The mass of Titan is ^Vo" that of Saturn. The 
orbit of Japetus, the outermost of all the satellites, is inclined 
about io° to the plane of Saturn's ring system. There is much 
uncertainty about the size of all these bodies, Pickering's pho- 
tometric determinations in 1877-78 making them less than half 
the diameters above given. Hyperion is the smallest satellite, 
and is probably not over 500 miles in diameter. Mimas comes 
next in size, its diameter being about \ greater than that of 
Hyperion. Eclipses of some of the satellites, and transits, 
particularly of Titan, Rhea, Tethys, and Dione, and of their 
shadows across the ball of the planet, have occasionally been 
observed, near the times (about 15 years apart) when the Earth 
is passing the planes of their orbits; but these phenomena 
require telescopes of exceptional power. — D. P. T. 



132 Stars and Telescopes 

interpreted to mean ' Annulo cingitur tenui piano 
nusquam cohaerente, ad eclipticam inclinato. , (It 
is surrounded by a thin, plane ring, nowhere adher- 
ing to it, and inclined to the ecliptic.) The explana- 
tion is given in his Sy sterna Satumium, published in 
1659, in which he refers to the observations of 
William Ball in England as confirming his own. In 
1676 Cassini in France perceived that there was a 
division in the ring. The inner ring of these two 
is perceptibly brighter than the outer, and it ap- 
pears that Campani at Rome, so early as 1664, na d 
noticed the greater brightness of the interior portion 
of the ring, though he failed to recognize an actual 
division between the two parts thus distinguished. 
Other smaller divisions have been noticed since, par- 
ticularly one in the outer ring by Encke in 1837. 
But the most remarkable recent discovery in this 
system of rings is that technically called the 6 dusky 
ring,' inside the two bright rings. This was first seen 
in 1850 by the Bonds of Cambridge, U. S., though 
there are several indications that a shading of the 
inner bright ring toward the planet had been noticed 
long before. Galle had in fact called especial atten- 
tion to it under this description in 1838. Lassell 
compared the dusky ring to ' something like a crape 
veil covering a part of the sky within the inner ring ' ; 
and its transparency was afterward noticed. 35 The 

35 According to D r Otto Struve's notation, adopted by 
astronomers generally, the rings are called A, B, and C, the last 
being the dusky ring, and A the outermost one. The luminous 
rings of Saturn differ greatly in brightness, the outer one being 
much fainter ; and having at times a very narrow, and proba- 
bly non-permanent, division about midway in it. The inner 
bright ring, area for area, is several times brighter than the 
outer one ; and the innermost, or dusky ring appears to be 




(Jean Dominique Cassini (1625-1712), whose chief claim to distinction 
rests on his discoveries in the Saturnian system, was earlier known as a 
student at Genoa, and a professor at Bolcgna, where his first astronomi* 
cal work was a discussion of the comet of 1652. Close observation tipon 
Jupiter a?id Mars enabled him to ascertain their periods of rotation in 
1665. Astronomical refraction, the distance of the S?<n, libration of the 
Moon, the zodiacal light, and measurement of a meridian arc were 
among the fertile stibjects of his investigation. Cassini's son and great- 
grandson were also directors of the Paris Observatory down to 1845, and 
his grandson likewise was engaged in the pursuit of science, though never 
director. Cassini also constructed tables of the motion of JupiteSs 
satellites. A It hough a lifelong observer, he availed himself of but few of 
the instrumental advances set on foot in his day) 




D E OTTO VON STRUVE AT THE EYE-PIECE OF THE 30-INCH TELESCOPE 

AT PULKOWA 
(Object glass by Alvan Clark & Sons ; mounting by the Repsolds) 



134 Stars and Telescopes 

Saturnian ring system, which has in so many ways 
been an enigma to astronomers, is now regarded as 
consisting of an innumerable multitude of very small 
satellites, so arranged as to present at a distance the 
appearance of a thin flat ring, with several narrow 
divisions in its breadth. Doubtless the peculiar 

immediately joined to it, the interior bright ring generally 
seeming to be darker on its inner edge, as if shading into the 
dusky ring. Kirkwood has explained the existence of divi- 
sions in the rings as due to perturbations in their substance 
caused by satellite attraction exerted in narrow zones where 
there would be a relation of simple commensurability with the 
periods of certain satellites, chiefly Mimas ; these divisions 
being analogous to the well-known gaps in the group of small 
planets caused by the perturbative action of Jupiter. 

The partial transparency of the dusky ring, so well shown 
in the illustrations on page 127, where the outline of the ball 
of Saturn is readily seen through this ' crape veil,' was excel- 
lently demonstrated by observations made by Mr Barnard 
with the 12-inch telescope of the Lick Observatory, 2d Novem- 
ber 1889, during an eclipse of Japetus in the shadow of the 
Saturnian system. As the satellite passed through the shadow 
of the dusky ring, its light grew fainter and fainter on ap- 
proaching the shadow of the bright ring, showing that the 
particles of this semi-transparent veil are more thickly strewn 
as the bright ring is approached. That the latter is fully as 
opaque to the Sun's rays as the globe of Saturn itself was 
convincingly shown by the complete disappearance of Japetus 
immediately on entering the shadow of the bright ring. Also 
the blackness of its shadow on the ball emphasizes the opacity 
of the substance composing this ring. In the same year Pro 
fessor Keeler examined the spectrum of the Saturnian rings 
with the 36-inch telescope of the Lick Observatory, but found 
no trace whatever of any such bands as are strongly marked in 
the spectra of Jupiter and the ball of Saturn; so that there 
can be no atmosphere about the ring. Also in 1895, hy a neat 
adaptation of Doppler's principle to an interpretation of the 
distorted spectra of the planet and its ring-system, he demon- 
strated anew the meteoric constitution of the rings ; for he 
proved that their inner edges revolve more swiftly round the 
planet than their outer edges do. — D. P. T. 



The Planets 135 

appearance of the dusky ring is due to the tiny satel- 
lites of which it is composed being much more scat- 
tered than those forming the bright rings. The outer 
diameter of the exterior ring amounts to 173,000 
miles, and the breadth of this ring is somewhat more 
than 10,000 miles. The outer diameter of the interior 
bright ring is 145,000 miles, and its breadth is 16,500 
miles. The distance of Mimas, the innermost satel- 
lite, from the exterior ring is 31,000 miles, and an 
interval of nearly 10,000 miles divides the dusky 
ring from the ball of the planet. The rings and 
satellites all revolve around Saturn in planes making 
only small angles with the planet's equator. 36 

35 Saturn's ring is sometimes totally invisible, except in very 
large telescopes ; and then, even with these, it can be seen only 
as depicted in the lower figure on page 127. This most interest- 
ing phenomenon takes place when the Earth reaches the plane 
of the ring (for this object is so thin that it does not fill an 
appreciable angle when seen edge on); when the plane of 
the ring is directed toward the Sun (for then its edge only is 
illuminated, and the reflected light is very feeble) ; and when 
Sun and Earth are on opposite sides of the ring (for its unillumi- 
nated side is then toward us). As the plane of the ring always 
remains parallel to itself, the epochs of disappearance are 
nearly 15 years apart, this interval being about one half the 
periodic time of Saturn. The two disappearances of the rings 
in 1861-62, many weeks in duration, were excellently observed. 
The subsequent recurrences, in 1878 and 1891-92, were short, 
and could not be well seen because Saturn was too near con- 
junction with the Sun. But about the middle of 1907 will 
occur the next disappearance, with a repetition in a general 
way of the phenomena of 1861-62, and with Saturn very favor- 
ably placed for observation. 

Our present knowledge of the constitution of the Saturnian 
rings has been attained through the researches of La Place, 
who showed that the rings could not be solid, because even the 
attractions of the external satellites would be sufficient to rup- 
ture them; of the late Professor Benjamin Peirce of Harvard 
College, whose investigation of the dynamics of the rings led him 



136 



Stars and Telescopes 



Beyond the orbit of Saturn are two large planets, 
Uranus and Neptune, the existence of which was not 



% .*^> s;:V 



J 



BEN T JAMIN PEIRCE (1809-1880) 



to the view that they 
must be fluid; and of 
Clerk Maxwell 
whose researches in 
1857 showed the incon- 
clusiveness of both pre- 
viously mentioned hy- 
potheses, and estab- 
lished on a firm basis 
the present theory of a 
vast shoal of clustering 
meteors, all revolving 
round Saturn in orbits 
of their own, as if actual 
satellites. Particles on 
the inner edge of the 
dusky ring, then, must 
revolve round the planet 
in 5 h 5o m ; while the pe- 
riodic time of those 
making up the outer edge of the outer ring is I2 h 5™. Probably 
the rings are slightly eccentric about the ball. . According to 
H. Struve, the entire mass of the ring system cannot exceed -g-y^ 
that of the planet ; Bessel had, in 1831, estimated it as TTT , 
and M. Tisserand in 1877, as ^20- 

The meteoric constitution of the rings is farther demonstrated 
from what is technically termed ' Roche's limit,' equal (for 
each planet) to 2.44 its radius; and Professor Darwin has 
pointed out that no large satellite can circulate round a planet 
inside this limit, because the known action of tide-producing 
forces would tear it into small fragments. As the Saturnian ring 
system lies wholly inside this critical limit, even the periphery 
of the outer ring lying about 2,500 miles within it, the conclu- 
sion is justifiable that the rings are composed of particles too 
small to be disrupted by planetary tides — of 'dust, rocks, and 
fragments.' Secular changes in the ring system are doubtless 
taking place; and the observations of the middle of the 20th 
century may, on comparison with those of the past, suffice to 
disclose such slowly progressive variations : perhaps a ninth 
satellite is in process of formation. — D. P. T. 






The Planets 137 

known to the ancients. Uranus was discovered by- 
Sir William Herschel while observing at Bath, 13th 
March 1781, and at first supposed by him to be a 
slowly moving comet. Its planetary character was. 
established as soon as the nature of its orbit became 
approximately known; and the principal credit of 
pointing this out is due to Lexell, whose name is 
more generally known by connection with the comet 
of 1 7 70, the remarkable story of which is told in a 
later chapter. Herschel proposed to name the new 
planet Georgium Sidus, or the Georgian Star, in honor 
of his royal patron, George the Third, while others 
preferred to call it after the discoverer ; but when the 
name Uranus was suggested, it soon obtained general 
acceptance. This planet takes 84 of our years to 
revolve round the Sun, from which it is distant about 
1,782 millions of miles. It was seen several times 
before Herschel's discovery, but always supposed to 
be a fixed star ; the first of these observations was by 
Flamsteed in 1690. Its mean diameter is 32,000 
miles. 

Some recent observations made by Professor 
Schiaparelli at Milan and by Professor Young at 
Princeton tend to confirm results obtained by Madler 
at Dorpat in 1842-43, that the polar compression of 
Uranus is about one twelfth, or greater than that of 
any other planet except Saturn. Markings have been 
noticed on its surface which indicate that Uranus has,, 
like Jupiter and Saturn, a rapid rotation, performed in 
a period of about ten hours. This rotation, however, 
takes place in a direction nearly perpendicular to the 
plane of the planet's orbit. The density of Uranus is 
a little less than that of Jupiter, and nearly one fourth 
that of the Earth ; while its mass is rather less than 
the twentieth part of that of the ' giant planet.' 



133 



Stars and Telescopes 



Early in 1787, Sir William Herschel discovered 
two satellites revolving round Uranus ; he afterward 
thought he had discovered four more, but the exist- 
ence of these has never been confirmed. Small 
fixed stars near the planet were probably mistaken 

THE SATELLITES OF URANUS 



Name of 

Satellite 


Date of 
Discovery 


Distance from 
Centre of Uranus 


Sidereal Period of 
Revolution 


In Miles 


In Arc 


Ariel 


14 Sept. 1847 


120,000 


rt 

13.8 


d 
2 


h m s 
12 29 21. 1 


Umbriel 


8 Oct. 1847 


167,000 


19.2 


4 


3 27 37.2 


Titania 


11 Jan. 1787 


273,000 


31-5 


8 


16 56 29.5 


Oberon 


11 Jan. 1787 


365,000 


42.1 


13 


11 7 6.4 




for satellites. But two other satellites, additional to 
Herschel's first two, were discovered by Lassell 
toward the end of 1851; and on 
removing his telescope temporarily 
to Malta the following year in order 
to profit by its transparent sky, he 
succeeded in determining theii 
periods with considerable accuracy. 
These two, which are interior to 
Herschel's two, were named Ariel 
and Umbriel ; while the others 
received the designations Titania 
and Oberon. It is not possible to measure accurately 
the sizes of these distant and comparatively small ob- 
jects, but Ariel and Umbriel are estimated to be about 
500 miles, and Titania and Oberon about 1,000 miles 



URANUS IN 1884 
{The Brothers Henry) 

\Earth on same scale, the 
size of a small letter ' o ' 
in the foot-note opposite) 



The Planets 139 

in diameter. Their motions are nearly perpendicular 
to the plane of the planet's orbit, and are performed 
in the reverse direction to that of all known planets, 
and of the satellites of all the planets interior to 
Uranus. 37 

37 Uranus on clear, moonless nights is bright enough to be 
seen without a telescope ; but one must know from the Ephe- 
mei'ts just where to look, as it is not far from the limit of visi- 
bility with the naked eye. Its stellar magnitude is 5J, and 
does not vary" greatly from opposition to conjunction. This 
exceeding faintness, relatively to Saturn, is partly due to the 
remoteness of Uranus, which is the only planet whose distance 
is more than double that of its next interior neighbor. The 
inclination of the orbit of Uranus to that of the Earth is the 
least of all the planets, being only j°. Professor Young, who 
observed this distant member of the solar system in 1883, with 
the 23-inch Princeton telescope, saw faint belts upon its disk, 
and found its ellipticity to be T a ? . Professor Schiaparelli 
the year before had found the degree of oblateness expressed 
by tt> and both series of observations indicate that the 
planet's equator coincides with the orbits of the satellites. 
M. Perrotin, formerly of the Observatory at Nice, and his 
assistant, the late M. Thollon, discovered on Uranus in 1884 
a white spot, whose reappearances indicated a rotation of the 
planet in about ten hours, a result needing confirmation. 
Five years later, with the 30-inch refractor at Nice, the belts 
seemed only a few degrees inclined to the plane of the satel- 
lite orbits, and the oblateness was not less than ■£$. 

The paths of the satellites of Uranus are sensibly perfect 
circles ; and in particular the orbits of Oberon and Titania 
Professor Newcomb ( Washington Observations for 1873) f° un d 
to be more nearly circular than in the case of any of the large 
planets of our system. Also these orbits have no discernible 
mutual inclination. The motions of the satellites lead to a 
mass of Uranus equal to 22J00 that of the Sun. Professor 
Pickering's determinations of the diameters of the outer satel- 
lites from photometric measures in 1878 gave, for Titania 
590 miles, and for Oberon 540 miles. Indications are that the 
inner satellites, Ariel and Umbriel, have a diameter about half 
as great ; and probably the combined mass of the satellites does 



140 Stars and Telescopes 

We now come to Neptune, the most distant known 
planet of all. When Bouvard was forming his Tables 
of planetary movements, about 40 years after the dis- 
covery of Uranus, he found it impossible to reconcile 
the observations of that planet since its discovery with 
the earlier observations made at various times when it 
was supposed to be a fixed star. Therefore, in forming 
his Tables, he rejected the latter altogether, and made 
use of the former only ; but stated in doing so that he 
left it to future time to determine whether the diffi- 
culty arose from inaccuracy in the older observations, 
or whether it depended on some extraneous and un- 
perceived influence which might have acted on the 

not exceed 13^00 that of the planet. At present the apparent 
orbits of the satellites of Uranus are ellipses of small eccentri- 
city, and large telescopes will now show these bodies at every 
point of their paths about the planet. In 1903 the Earth will 
be near the pole of these orbits, so that they will appear 
almost perfectly circular. The outer, or Herschelian satellites 
have been seen under perfect atmospheric conditions with a 
6-inch telescope ; but the inner ones, Ariel and Umbriel, require: 
for their certain observation the largest of telescopes and the 
keenest of eyes. Variability in the light of Ariel is suspected. 

The spectrum of Uranus has been critically surveyed by 
D r Huggins with the assistance of photography, and by 
D r Vogel, Professor Keeler, and M r Taylor. Professor 
Keeler's optical observations of the spectrum of Uranus with 
the 36-inch Lick telescope give ten broad diffused bands, from 
C to F y indicating strong absorption by a dense atmosphere 
differing greatly from ours ; and the presence of these bands 
accounts for the invariable sea-green tint of the planet. The 
substance producing the absorption is not yet identified, and 
the darkest band, about midway between C and D, is also- 
shown in exactly the same position in the spectra of Jupiter 
and Saturn. So great is the light-gathering power of the Lick 
glass that even the outer satellites of Uranus, faint as they are, 
gave spectra which Professor Keeler could just recognize as 
continuous, — D. P. T, 




2 

I 
> 



■8 



142 



Stars and Telescopes 



planet. The question as to the nature of the cause 
was soon settled by the rapidly increasing deviation of 
Uranus from the course marked out for it by the Tables 
based upon observations between 1781 and 182 1 ; 
nor could it reasonably be doubted that the cause 
was the perturbing attraction of a planet still farther 
from the Sun, and never (so far as was known) 
hitherto observed. 




LE VERRIER (181I-1877) 

But the problem of calculating the place of an 
unknown planet by simple knowledge of its influence 
upon another, staggered the few mathematical astron- 
omers who were capable of attacking it, most of 
whom were already deeply engaged in labors too 






The Planets 



143 



essential and exacting to bear an interruption of the 
length which its solution would seemingly demand. 
In 1843-45, however, it was taken up by two young 
mathematicians, one in England the other in France, 
whose names are now famous wherever astronomy 
is studied. The former, John Couch Adams, for a 
long time Professor of Astronomy at Cambridge, and 




ADAMS (1819-1892) 



Director of the Observatory there, died 21st January 
1892; the other, Urbain Jean Joseph Le Verrier, 
was for many years Director of the National Observa- 
tory at Paris, where he died 23rd September 1877. 
We cannot enter here into the history of their recon- 
dite investigations ; the approximate place of the 
unknown planet was carefully determined by both 



144 Stars and Telescopes 

independently, and Challis at Cambridge began 
searching for it by its motion, 29th July 1846. 
During several weeks he mapped down all the stars 
visible in a considerable tract of the heavens around 
the place indicated by Adams, with the intention of 
comparing afterward the places of all these stars and 
ascertaining which of them had moved ; and he thus 
obtained several positions of the planet. But before he 
had completed his charts in this way, news arrived that 
Galle at Berlin had discovered the planet, 23rd Sep- 
tember 1846, on looking for it in the place pointed 
out by Le Verrier, who had suggested that the planet 
might be distinguished by its disk among the fixed 
stars in the neighborhood of the calculated place. Its 
appearance at once showed that it was the object of 
search * also it was wanting in a map (then recently 
made by Bremiker) of the stars in that part of the 
heavens, and which had just been received at the 
Berlin Observatory. The next evening, 24th Septem- 
ber, the alteration in its place put its planetary char- 
acter beyond a doubt. Subsequently the name ' Nep- 
tune ' (one of the names suggested for Uranus when a 
designation for that planet was under discussion) was 
by common consent adopted. 

Neptune occupies 164! °f our Y ears m revolving 
round the Sun, at a distance of 2,792 millions of 
miles, about 30 times that of the Earth. The eccen- 
tricity of its orbit is the smallest of those of all the 
principal planets, with the single exception of Venus. 
The diameter of Neptune is about 34,800 miles, so that 
its volume or bulk is 85 times that of the Earth, but 
only about T ^ that of Jupiter. Its density is nearly the 
same as that of Uranus, and its mass is to that of the 
Sun in about the proportion of 1 to 19,380. Being 



The Planets 145 

at so great a distance, it has not yet been found possi- 
ble to perceive any spots or markings on the surface ; 
so that its time of axial rotation is unknown to us. 
Like the other large planets, it probably rotates much 
more rapidly than the Earth. ^~- 

Only one satellite of Neptune is known. This was 
discovered by Lassell, 10th October 1846, very soon 
after the discovery of the planet itself. Being visible 
at so great a distance, it is probably the largest satel- 
lite in the solar system. Like the satellites of Uranus, 
it moves in a reverse direction to that of the planetary 
motions, and its orbit is very much inclined to those 
of the planets (about 55 to that of Neptune itself). 
Its distance from the centre of Neptune is 225,000 
miles, and its time of revolution is 5 d 2i h 2 m 38 s .o. 
If this planet has other satellites, as is possible, they 
must be much smaller, since none have hitherto been 
detected with the powerful telescopes which have 
been brought into use in recent years. 38 

38 So remote is Neptune that its disk, although more than 
4^ times the actual diameter of the Earth, shrinks to an angle 
no greater than that which a nickel 5-cent piece would fill, if 
held up a mile distant. According to Professor Pickering, 
its stellar magnitude is 7.63, so that it can never be visible 
to the unaided eye. 

Portraits of both the theoretical discoverers of Neptune 
have been given on pages 142 and 143. For the fullest ac- 
count of their great discovery it is necessary to consult the 
original papers; but D r Gould has given a complete resume 
in his Report on the History of the Discovery of Neptune (Wash- 
ington 1850). As in the case of Uranus, so with Neptune, it 
was soon found that the new planet had been accidentally 
observed as a star (by Lalande in 1795), so tnat observations 
of Neptune now extend through more than a century, or an 
arc of about 225 round the Sun as a centre. Among Ameri- 
can astronomers who performed a zealous and important part 
in the researches on Neptune's orbit, immediately after its dis- 
s& t — 10 



146 



Stars and Telescopes 



covery, must be mentioned Peirce and Walker; and in 1866 
were published Professor Newcomb's Tables of Neptune, which 
provided a good representation of the planet's motion for about 
15 years. In 1877, Le Verrier's Tables appeared, founded 
upon many years more observations than the preceding; but 
already, in less than 25 years, the planet is beginning to deviate 
widely from their prediction, and the theory of Neptune's mo- 
tion is at the present time undergoing a second revision by 
Professor Newcomb. Neptune's path round the Sun, like that 
of Jupiter, is but slightly removed from the invariable plane of 

the solar system, 
this plane in fact 
lying about mid- 
way between the 
orbits of Neptune 
and Jupiter. 

Probably the sen- 
sibly circular path 
of Neptune's sat- 
ellite is inclined by 
a large angle to the 
planet's equator; 
and the motion of 
its orbit plane, as 
established by ob- 
servation, has 
been accounted 
forbyTissERAND, 
who supposes an 
oblateness of Nep- 
tune equal to 
about g^^he equa- 
torial protuber- 
ance causing the 
orbit plane to par- 
take of a regressive motion round the pole of the planet in a 
period exceeding 500 years. At the present time the path which 
the satellite seems to describe about its primary is so open that 
this minute object is at no time overpowered by the planet's 
rays ; any good telescope above 12 inches of aperture will show 
it. The diameter of Neptune's satellite, as determined by Pro- 
fessor Pickering from photometric measures in 1878, is 2260 
miles. Critical search for an additional satellite, both optically 




F. F. TISSERAND (1845-1896) 



The Planets 



147 



and by means of photography, has shown that there is no such 
body, unless its dimensions are very minute. Neptune's spec- 
trum closely resembles that of Uranus, and probably the planet 
is surrounded by a dense atmosphere. — D. P. T. 



The extensive popular literature of the planets can only be 
indicated here by tabulated reference to the pages of Poole's 
Indexes to periodical literature : — 





POOLE'S Index to 




Annual Literary 




Periodical Literature 


FLETCHER'S 


Index for 


Subject 

of 

Reference 




Index to 

General 

Literature 

(Boston 1893) 




Vol. 1 
1802-81 


1st Sup- 
plement 
1882-86 


2d Sup- 
plement 
1887-91 


3d Sup- 
plement 
1892-96 


1897 


1898 


1899 


Planets 


p. 1014 


P-343 


P- 333 


P-445 


p. 223 


p. 100 


p. 104 




Mercury 


824 


283 


274 






82 






Venus 


1366-7 


459 


448 


602 


299 


135 


140 




Mars 


804 


277-8 


269 


357 


184 


81 






Asteroids 


69 


25 


24 


33 


223 




104 




Jupiter 


699 


239 


233 


306 


157 


69 


7 1 




Saturn 


1152 


386 


375-6 


503 


253 


113 


116 




Uranus 


1359 


456 


446 




297 








Neptune 


906 


309 






223 









A thorough study of the planets will be greatly facilitated by 
reference to the following important papers, for the most part 
original sources. These lists need, however, to be supplemented 
by reference to current numbers of The Astrophysical Journal ', 
1 895-1 898: — 

INTRA-MERCURIAN PLANETS 

Le Verrier and Lescarbault, Comptes Rendus, xlix. and 1. 

(1859-60). Also Le Verrier, Ibid., 1876-78. 
Wolf, Handbuch der Mathematik, ii. (Zurich 1872), 326. 
Watson, Am. Jour. Scie?ice and Arts, cxvi. (1878), 230, 310. 
Swift, American Journal of Science and Arts, cxvi. (1878), 313. 
Peters, Astronomische Nachrichten, xciv. (1879), 3 2I > 337» 
Ledger, Lecture on Intramercurian Planets (Cambridge 1879). 
TlSSERAND, Anntiaire du Bureau, des Lo?tgitudes for 1882, p. 729. 
Newcomb, Astron. Papers of Am. Ephemeris, i. (1882), 474. 
Houzeau and Lancaster, Bibliographic Generate de V Astron- 

omie, ii. (Bruxelles 1882), 1090, contains nearly 150 titles. 
Bauschinger, Bewegung des Planeten Merkur (Munich 1884). 
Chambers, ' Vulcan/ Astronomy, i. (Oxford 1889), p. 75. 
Corrigan, Popular Astron. iv. (1897), 414; v. (1897). 



148 Stars and Telescopes 



Mercury 

Schroeter, Hermographische Fragmente (Gottingen 181 5-16). 

Le Verrier, ' Tables of its Motion,' Annates de V Observatoire de 
Pa ris, Mem oires v. (1859). 

Vogel, Bothka?np Beobachtungen, ii. (1873), I 33- 

Harkness and others, ' Transit 1878/ Wash. Obs. 1876, App. ii. 

Holden, I)idex of. . . Transits of Mercury (Cambridge 1878). 

Todd, ' Satellite/ Proc. A. A. A. S. xxviii. (1879), 74. 

NlESTEN, ' Transits 1600-2000/ Annuaire de VObs. Roy. Brux- 
elles, 1881, p. 192. 

Schiaparelli, Atti delV Accad. deiLincei, v. (1889), ii. ; Pop. Set. 
Monthly, xxxvii. (1890), 64 ; Astron. A r achr. exxiii. (1890), 241. 

Clerke, ' Rotation/ four. Brit. Astron. Assoc, i. (1890), 20. 

Harzer, ' Motion perihelion/ Astron. A T achr. exxvii. (1891), 81. 

Ambronn, 'Diameter/ Astron. Nachr. exxvii. (1891), 157. 

Trouvelot, Les Planetes Venus et Mercure (Paris 1892). 

MtJLLER, 'Magnitudes/ Pub/. Obs. Potsdam, viii. (1893). 

Newcomb, Elemeiits of the Four Inner Planets and the Funda- 
mental Constants of Astronomy (Washington 1895); 'Small 
Planets between Mercury and Venus/ p. 116. 

Lowell, The Atlantic Monthly, lxxix. (1897), 493- 

Lowell, Popular Astrono?ny y iv. (1897), 360. 

Lowell, ' New Observations/ Mem. Am. Acad. xii. (1898), 433. 

Villiger, Ann. k. Steruzvarte, iii. 301 (Munich 1898). 

Venus 

Schroeter, Aphroditographische Fragmente (Helmstedt 1796). 
Le Verrier, ' Tables of its Motion/ Annates de V Observatoire de 

Paris, Memoir es, vi. (1861). 
Lyman, C. S., Am. Jour. Sci. xliii. (1867), 129; ix. (1875), 47- 
Kaiser, ' Diameters of Planets ,' Leyden Observations, iii. (1872). 
SAFARIK, Report British Assoc. Adv. Sci., 1873, P- 4°4- 
VOGEL, Bothkamp Beobachtungen, ii. (1873), 118. 
Proctor, The Universe and the Coming Tra7isits (London 1874). 
Forbes, Transits of Venus (London 1874). 
Schorr, Der Venus??iond (Brunswick 1875). 
Hartwig, Publ. Astron. Gesellschaft, xv. (Leipzig 1879). 
PERROTIN, Comptes Rendus, cxi. (1890), 587. 
Terby, Bulletins Acad. Roy ale de Belgiaue, xx. (Brussels 1890). 
Schiaparelli, Rend, del R. 1st. Lombardo, xxiii. (1890), ii. 
Clerke, A. M., four. Brit. Astron. Assocn. i. (1890), 20. 



The Planets 149 

Newcomb, ' Transits/ Ast. Papers Am. Eph. ii. (1890), 259. 
Auwers, 'Diameter/ Astrou. Nachr. cxxviii. (1891), 361. 
Loschardt, Sitz. k. Akad. Wiss., c. (Vienna 1891), 537. 
Niesten, Rotation de la Planete Venus (Brussels 1891). 
Trouvelot, Nature, xlvi. (1892), 468. 
Clerke, E. M., The Planet Venus (London 1893). 
Flammarion, Comptes Rendus, cxix. (1894), 670. 
Brenner, Astronomische A T achrichten, cxxxviii. (1895), x 97« 
Schiaparelli, A stronomische Nachrich ten, cxxxviii. (1895), 2 49- 
Vogel, ' Planetary Spectra/ A sir op hys. Jour. i. (1895), 196, 273 
Lowell, Popular Astronomy, iv. (1896), 281. 
Antoniadi, ' Rotation/y<?^;-. Brit. Astr. Assoc, viii. (1897), 43. 
Lowell, The Atlantic Monthly, lxxix. (1897), 327. 
Flammarion, Knowledge, xx. (1897), 2 34> 258. 
Chandler, 'Rotation/ Popidar Astronomy, iv. (1897), 393. 
Stoney, ' Atmospheres/ Astrophysical Journal, vii. (1898), 25. 
Douglass, ' Markings/ M. N. Roy. Astr on. Soc. lviii. (1898), 382. 

Mars 
For the literature of this planet see page 178. 

THE SMALL PLANETS 

Gould, The Ajnerican Journal of Science, vi. (1848), 28. 
d'Arrest, Ueber das Syste?n der kleinen Planeten (Leipzig 1851 ). 
Newcomb, Mem. A??z. Acad. Arts and Sciences, viii. (1861), 123. 
Stone, E. J., M. N. Royal Astron. Society, xxvii. (1867), 3° 2 - 
Callandreau, Revue Scientifique, xviii. (1880), 829. 
Niesten, Annuaire de V Observatoire Royal de Bruxelles for 1881. 
Svedstrup, Astronomische Nachrichten, cxv. (1886), 49. 
ParKHURST, Annals Harvard College Observatory, xviii. (1888). 
LlAlS and Cruls, Annates de VObs. de Rio de Janeiro, iv. (1889). 
Schmidt, R., Publ. Astron. Society Pacific, ii. (1890), 238. 
Tisserand, Popular Science Monthly, xxxix. (1891), 195. 
KlRKWOOD, Proc. Am. Phil. Society, xxx. (1892), 269. 
Backlund, Mem. Acad. Set. St Petersbourg, xxxviii. (1892). 
Todd, Astronomy and Astrophysics, xii. (1893), 3 X 3- 
Callandreau, Comptes Rendus, cxviii. (1894), 751. 
RoszEL,y. H. Univ. Circ. xiii. (1894), 67 : xiv. (1895), 2 3- 
Charlois, Bulletin Astron. xi. (1894) ; xiii. (1896). 
Zenger, Bulletin Societe Astronomique de France (1895), 243. 
Mascart, ' Small Planets/ Bulletin Astron. xv. (1898), 235. 
Crommelin, ' Planet D Q/ Knowledge, xxi. (1898), 250. 



i5° 



Stars and Telescopes 



Jupiter 

Somervtlle, Mechanism of the Heavens (London 1831). 
De Damoiseau, Tables Ecliptiqiies Satellites (Paris 1836). 
Engelmann, Helligkeitsverhdltnisse der Jupiterstrabanten 

(Leipzig 1871). 
Lohse, Bothkamp Beobachtnngen, i. (1S72) ; ii. (1873). Also 

Publ. Astrophys. Observ. Potsdam, i. (1879) ; iii. (1882). 




MARY SOMERVILLE (1780-1872) 



Glasenapp, Cpaeneme HadAwdemu 3am.wbmu CnymHUKOffb 

IDnumepa (C.-Uemep6ypvb 1874). 
Downing, Abstract of foregoing, Observatory, xii. (1889), 173. 
Rosse, Monthly A r otices Royal Astronomical Society, xxxiv. ( 1874). 
Bredichin, Ann. de V Observatoii'e de Moscou, ii.— vi. (1875-80). 
Todd, Continuation of De Damoiseau's Tables Ecliptiqiies to 

1900 (Washington 1876). 
Le Verrier, ' Tables of its Motion/ Annates de V Observ atoire 

de Paris, Mhnoires, xii. (1876). 



The Planets 1 5 1 

Denning, Science for All, part xxx. (London 1SS0), 169. 
Souillart, Memoirs Royal Astronomical Society > xlv. (1S80). 1. 

TROUVELOT, Proc. Am. Acad. Arts and Sciences, viii. ( iSSl ), 299. 
Kempf, ' Mass,' Publ. Astrophys. Observ. Potsdam, iii. (18S2). 
Denning, * Summary of Markings and Rotation-periods,' 

Nature i xxxii. '(1SS5), 31; Observatory, ix. (1SS6), iSS ; xi. 

(iSSS), SS, 406; xiv. (1S91), 329. 
WILLIAMS, The Observatory, ix. (1SS6), 231. 
Lamey, Comptes Rendns, civ. (1SS7), 279, 613. 
Souillart, Mem. Academic des Sciences, xxx. (Paris 1887). 
Backlund, 'Satellites,' Bulletin Astronomique, iv. (1887), 321, 
Barnard, Publ. Astron. Society Pacific, i. (1SS9), 89. 
Landerer, Estudios geometmcos sobre el sistema de los satellites, 

(Barcelona 18S9). Co?nptes Rendus, cxiv. (1S92), S99. 
Williams, Zenographic Fragments (1SS9). 
Waugh, _/?*//'. Brit. Astron. Association, i. (1S90). 
Keeler, Publications Astron. Society Pacific, ii. (1S90), 286. 
Hill, ' A New Theory of Jupiter and Saturn,' Astron. Papers 

Am. Ephemeris, iv. (Washington 1S90). 
Schaeberle, Campbell, Pub. Ast. Soc. Pacific, iii. (1S91), 359. 
Clerke, E. M., Jupiter and his System (London 1S92). 
Schur, Astronomische Nachrichten, cxxix. (1S92), 9. 
Tisserand, ' Fifth Satellite,' Comptes Rendus, cxvii. ( 1S93). I02 4= 
Pickering, W. H., Ast. and Astro-Phys. xii.-xiii. (1S93-94). 
Williams, Freeman, and others, Mem. Brit. Astron. Assoc, i. 

(1S93), 73 5 ii- (1S94), 129. 
Hough, ' Constitution of Jupiter,' Astronomy and Astro-Physics, 

xiii. (1S94), 89; Popular Astronomy, ii. (1S94), 145. 
Barnard, Astron. and Astrophysics, xiii. (1894). 
Maunder, Green, Knowledge, xix. (1896], 4, 5. 
Pottier, ' Satellites,' Bulletin Astronomique, xiii. ( 1S96), 67, 107. 
FLAM MARION, Bulletin Soc. Astron. France, July 1S96. 
Belopolsky, • Rotation,' Astron. A'ach. cxxxix. (1896), 209. 
Douglass, ' Satellite in,' Pop. Astron. v. (1S97). 308. 
Brenner, ' Observations 1S95-96,' Vienna Acad. Sci. 1S97. 
Denning, 'Red Spot,' Nature, lviii. (1S9S), 331. 
Williams, 'Rotation,' M. N. Roy. Ast. Soc. lviii. (1S9S), 10. 
Denning, M. X. Roy. Ast. Soc. lviii. (1S98), 4S0, 4S8. 

Saturn 

Bond, G. P., ' Rings of Saturn,' Am. Jour, of Sci. lxii (1S51 ), 97. 
Dawes, American Journal of Science, lxxi. (1S56), 158. 



152 



Stars and Telescopes 



Watson, ' Ring,' Mo. Not. Roy. Astr. Soc. xvi. (1856), T52. 

Maxwell, Stability of Saturn's Rings (Cambridge 1859). 

Proctor, Saturn and its System (London 1865). 

Peirce, ' Saturnian System/ Afem. Nat. Acad. Sciences, i. (1866). 

Hirn, Anneaux de Saturne (Colmar 1872). 

Bessel, Abhandlungen, i. (Leipzig 1875), pp. no, 150, 319. 

Trouvelot, Proceedings Am. Acad. iii. (1876), 174. 

Le Verrier, ' Tables of its Motion/ Annates de V Observatoire 

de Paris, Memoires, xii. (1876). 
PrCKERlNG, E. C, Annals Harvard Observatory, xi. (1879), 269. 
Hall, ' Six inner Satellites/ Washington Observations 1S83. 

Trouvelot, Bulletin Astron. i. 

(1884), 527; ii- (1885), 15. 
BAILLAUD, Bulletin Astrono- 
mique, i. (1884), 161 ; ii. 
(1885), 118. 
Meyer, Le Systeme de Saturne 

(Geneva 1884). 
PoiNCARE, Bulletin Astrono- 
mique, ii. (1885). 
Seeliger, Mem. de V Acad. 
Sciences de Baviere (Munich 

i83 7 ). 

Gore, J. E., Planetary and Stel- 
lar Studies (London 1888). 
Elger, Month. Notices Royal 
Astron. Society, xlviii. (1888), 
362. 

Perrotin, 'Rings,' Comptes Rendus, cvi. (1888), 1716. 

STRUVE, H., Observations de Poulkova, Supplement, i. (1888); ii. 
(1892). Also M. N. Roy. Astron % Society, liv. (1894), 452. 

Tisserand, Annates de V Observatoire de Toulouse, ii. (1889); 
Bulletin Astronomique, vi. (1889), 383, 417. 

Hall, A., jr., Trans. Ops. Yale Univ. i. (1889), 107. 

Darwin, ' The Rings/ Harper's Magazine, lxxix. (1889), 66. 

Anding, Astronomische Nachi'ichten, exxi. (1889), 1. 

OUDEMANS, M. N. R. A. S.xlix. (1889), 54 ; Astron. Nach. 3074. 

Stroobant, Bulletins de V Acadhnie Royale Belgique, xix. (1890). 

Trouvelot, Bulletin Astronomique, vii. (1890), 147, 185. 

Newcomb, Astron. Papers Am. Ephemeris, iii. (1891), 345. 

Struve, H., Bulletin Acad. Sci. St Petersbourg, ii. (1891). 

Etchelberger, The Astronomical Journal, xi. (1892), 145. 

Green, Freeman, Mem. Brit. Astron. Assoc, ii. (1893), 1. 




WATSON (1838-1880) 



The Planets 



153 



WILLIAMS, Month. A r ot. Roy. Astron. Society, liv. (1894), 297. 
Olbers, ' Ring,' Sein Lebcn und Seine Werke (Berlin 1894). 
Pritchett, Ueber die Verfinsternngen der Saturntrabanten 

(Munich 1S95). 
Buchholz, * Eclipse of Japetus/ Astron. Nach. cxxxvii. (1895). 
Keeler, 'Ring Spectra/ Astrophys.Joitr. i. (1895), 416; ii. 63. 




olbers ( 1 758-1840) 



Witt, Himmel tend Erde, ix. (1896), 75, 121. 
Barnard, Pop. Astron. v. (1897), 285; M. N. R. A. S. lvi. 
(1896), 14; lviii. (1898), 217. 

Uranus 

Newcomb, ' Orbit of Uranus/ Smithsonian Contributions to 
Knowledge, xviii. (1872). 

Newcomb, 'The Uranian and Neptunian Systems,' Washing- 
ton Observations for 1873, Appendix I. 

Le Verrier, 'Tables of its Motion/ Annates de V Observatoire 
de Paris, Memoir es, xiv. (1877). 

SCHIAPARELLI, Astronomische Nachrichten, cvi. (1883), 81. 



154 Stars and Telescopes 

YOUNG, Astronomische Nachrichten, cvii. (1883), 9. 
Perrotin, Comptes Rendus, xcviii. (1884), 718, 967. 
Henry, Comptes Rendus, xcviii. (1884), 1419. 
Gregory, ' Uranus/ Nature, xl. (1889), 235. 
Lockyer, ' Spectrum/ Astron. Nach. cxxi. (1889), 3^9- 
HUGGINS, W. and M. L., Proceedings Royal Society, xlvi. (1889), 
231; also M. N. Royal Astrono?nical Society, xlix. (1889), 404. 
Keeler, Astrono?nische Nachrichten, cxxii. (1889), 401. 
Taylor, ' Spectrum,' M. N. Royal Astron. Soc. xlix. (1889), 4°5- 
Barnard, The Astro?iomical Journal, xvi. (1896). 

Neptune 
Loomis, 'History of its Discovery/ Am. Jo7ir. Sci. lv. (1848), 

187. Also Recent Progress of Astron o??iy (New York 1850). 
GOULD, History of the Discoz'ery (Washington 1850). 
Herschel, J. F. W., * Perturbation of Uranus by Neptune/ 

Outlines of Astro momy (London 1865), p. 533. 
NEWCOMB, ' Tables of its Motion/ Smithsonian Contributions to 

Knowledge, xv. ^Yashington 1867). 
Le Yerrier, * Tables of its Motion,' Annates de V Observatoire 

de Paris, Memoires, xiv. (1877). 
Peirce, Ideality in the Physical Sciences (Boston 1881), App. B. 
TlSSERAND, ' Satellite/ Comptes Rendus, cxviii. (1894), 1372. 
Struve, H., ' Satellite/ Mem. de V Acad. Sciences, xlii. (St. 

Petersburg 1894). 
LlAlS, ' Historia Descubrimiento/ A?iuario del Observatorio 

Astro?iomico Nacional de Tacubaya para el Aho de 1895, P- 2 47» 
ADAMS, Scie?itific Papers (Cambridge, Eng. 1896), i. 




newton's birthplace at woolsthorpe, Lincolnshire 

{On one end of the house are shown the sundials Newton 
made when a boy) 



CHAPTER XI 

THE RUDDY PLANET 



MARS, the earliest observation of which, b. c. 356, is its 
occupation by the Moon recorded by Aristotle, was 
first scrutinized with the telescope by Galileo, who discovered 
the planet's phases in 1610. The earliest sketch of its sur- 
face was made by Fontana, in 1636, though little or no detail 
was made out until 1659, when Huygens observed its markings 
clearly enough to show him that the period of rotation of Mars 
was about the same as that of the Earth. Seven years later 
Cassini discovered the well-known polar caps, and made the 
first determination of the axial 
period, 24 11 4o m , now known to 
be only -%fa part in error. 
Among other prominent ob- 
servers of the 17th century 
were Riccioli, Hooke. and 
Hevelius ; and in the __ '- 
Bianchini, Schroeter, and 
Sir William Herschel, who, 
beginning in 1777, first detect- 
ed, in 1783, the fluctuating di- 
mensions of the polar caps 
with the Martian seasons, de- 
termined the inclination of the 
planet's axis to its orbit, and 
measured the oblateness of 
Mars. 

Early in the 19th century came Flaugergues, Harding, 
and Arago who observed the planet for 36 years; and in 
1830-40, Beer and Maedler, who drew the first map of Mars, 
with the markings then known (among them Lacus Phcenicis) 
carefully set down in Arean longitude and latitude. Since their 
day Martian investigations have rapidly increased in fulness 
and importance, the chief observers down to the very favorable 




arago (17S6-1S53 



156 Stars and Telescopes 

opposition of 1862 being Sir John Herschel, Kaiser, Secchi 
who studied the colors of different regions, Lord Rosse, Las- 
sell, and Lockyer whose fine sketches inaugurated the modern 
standard of excellence. From that time onward, there have 
been critical observations by Dawes, Knob el, Trouvelot, 
Green, Terby, Niesten, Lohse, and others, culminating in 
the classic labors of Schiaparelli, begun at the memorable 
oppositions of the planet in 1877 and 1879. So abundant and 
careful have been the drawings of this planet in the past that 
many excellent maps of its entire surface have been made, by 
Kaiser (1864), Proctor (1867), Green (1877), Dreyer (1879), 
and in particular by Schiaparelli (1888), supplanting all 
others, from his elaborate sketches with the 18-inch Merz re- 
fractor of the Brera Observatory at Milan. D r Wislicenus 
of Strassburg has done excellent service by applying the mi- 
crometer to the more conspicuous markings, thereby establish- 
ing their accurate positions ; and it is no exaggeration to say 
that the areography of Mars is now better known than the 
geography of immense tracts of our own planet. 

Mars, although the nearest to the Earth of all the planets, 
Venus alone excepted, is an object by no means easy to ob- 
serve. To realize the extent of the difficulty, even under the 
best imaginable conditions of instrument and atmosphere, let 
any one with no previous knowledge of the Moon attempt to 
settle precise markings, colors, and the nature of objects on 
our satellite by simple scrutiny with an ordinary opera-glass. 
Indeed, the Moon would, for many technical reasons, prove the 
less perplexing, although the two cases would be quite parallel 
in so far as mere geometry is concerned. 

Sketches and Variations 

Personal differences affect all sketches of Mars unduly, and 
the delicate and changing local colors add much uncertainty. 
Still, the leading features of the planet's surface are well made 
out, and their stability leaves no room to doubt their reality as 
permanent planetary crust. Here, unfortunately, the great ad- 
vance in photographic application to astronomical requirements 
has not yet helped much, although excellent plates have been 
obtained by Professor Pickering, and at the Lick Observatory 
as well: the texture of the sensitized film is too coarse, and the 
image of the planet is too small and faint. The border of its disk 
is brighter than the interior, as the Lick photographs show ; 



The Ruddy Planet 



157 



but this brightness is far from uniform, and the variation is 
probably caused by the surface features of the planet. Also varia- 
tions of color in the markings of Mars depend upon the diurnal 
rotation of the planet and the angle of vision ; and changes of 
apparent brightness in certain regions are as well established as 
in the case of the Moon. Argyre /, for example, first observed 
bv Dawes, in 1S52, has often been seen by Schiaparelli to be 
reddish yellow"when near the central meridian, while again, after 
the planet's rotation has carried 
it round to the limb, it has ap- 
peared so brilliant as to be mis- 
taken at first for a polar cap. 
This skilful observer has also 
noticed similar changes, progres- 
sive in character, covering exten- 
sive continental regions. A small 
white spot, Nix Atlantica, first 
observed by him in 1877, then 
almost square, and more brilliant 
than any other part of the planet, 
became at subsequent oppositions 
nearly round, fluctuating in ap- 
pearance and brilliancy, and in 
18SS had entirely disappeared. 

Mindful of these obstacles in 
our own day, it is easy to see 

why the early telescopists failed to discern very much : all had 
not only that ever-present foe of the astronomer, the atmos- 
phere, to battle against, but the imperfections of their instru- 
ments were a farther and most serious handicap. Formerly 
observations of a near approach of Mars to the Earth would be 
made only from localities where observatories were previously 
established ; but the exceeding present interest in our neighbor- 
ing planet led to the building and maintenance of an observatory 
with a large and perfect telescope and a corps of astronomers 
at a mountain elevation in a clear and steady atmosphere, 
with the especial intent of a critical survey of the ruddy 
planet, during its recent and very favorable presentation in 
1894-95. Frequent allusion will be made in this chapter to the 
excellent work of M r Percival Lowell (at the observatory 
bearing his name, and temporarily located at Flagstaff, Arizona, 
elevation 7250 feet above sea level), and of his coadjutors, 
Professor W. H. Pickering and M r Douglass. 




kaiser (1808-1872) 



158 Stars and Telescopes 

General Topography 

The most casual observer of Mars would not fail to notice 
the striking difference between the brightness of the two hemi- 
spheres — the northern chiefly bright, and the southern pro- 
nouncedly dark. In fact, the light and dark regions are each 
approximately a hemisphere in area. Allowing that the cosmic 
conditions of Mars are still suitable for the existence of water 
and an atmosphere, though of no great density, it is an easy 
surmise, and perhaps the true one, that the lighter regions of 
the planet's face disclosed by the telescope are land and the 
darker water. The southern hemisphere of Mars, then, is 
principally water, and the northern continental land, precisely 
as in the case of the Earth (page 24) ; but while, on our globe, 
the proportion of land and water is about four to eleven, the 
surface of Mars shows water and land in very nearly equal 
amounts, with a slight preponderance of the latter. 

Mars, in its general topography, presents no analogy with 
the present scattering of land and water on the Earth. Fully 
one third its surface is the great Mare Australe, strewn 
with many islands, and apparently intersecting the continents 
by numerous divisions, narrowing northward and suggesting 
gulfs. There seems little reason to doubt that the northern 
regions, with their predominant orange tint, in some places a 
dark red and in others fading to yellow and white, are really 
continental ; and Professor Schiaparelli thinks that the Arean 
continents appear red and yellow because they are so in fact, 
atmospheric action having little or no influence upon their hue. 
Different from the Earth, the lands of Mars are mostly massed 
in a single vast continent, spotted with the great lakes Mare 
Acidalium and Lacus Niliacus, the former of which is found to 
be variable in area. Other extensive regions, for example, the 
islands of Mare Australe and Mare Erythraeiim, sometimes 
appearing yellow like continents, and again dark brown, are 
thought by Schiaparelli and Niesten to be vast marshes, 
the varying depth of water causing the diversity of color. 

The seas of Mars, generally brown mixed with gray, also 
vary in intensity from light gray to deep black ; it seems prob- 
able that only the darkest of dark regions may actually be deep 
water. The true aquatic character of the suspected seas would 
best be established by watching for the reflection of the solar 
image from them ; and M. Flammarion has calculated that 
under favorable circumstances the Sun x thus reflected, ought to 






The Ruddy Planet 159 

w 
shine as a star of the third magnitude ; but no such phenome- 
non has yet been observed. Professor Pickering's latest ob- 
servations incline him to the opinion that the permanent water 
area upon Mars, if it exists at all, is extremely limited. 

Axis and Polar Caps 

The axis of Mars pierces the northern heavens about mid- 
way between the two bright stars a Cephei and a Cygni 
(Deneb), and no precessional motion of the pole is yet made 
out. The waxing and waning of the polar caps, being largest 
near the end of the Martian winter and smallest near the end of 
summer, are phenomena which have long been well established. 
A brilliant white, they are generally thought to be composed 
of snow and ice ; and their existence is a most convincing 
argument for the reality of a Martian atmosphere, capable of 
transporting and diffusing vapor. 

The northern cap is centred on the north pole of the planet 
almost exactly ; and its gradual melting, observed by Schiapa- 
relli in 1882, 1884, and 1886, appeared to create a temporary 
zonal ocean, from which radiated many darkish streaks, con- 
necting southward with numerous round patches, called Makes' 
bv him, and ' oases ' by M r Lowell. Our knowledge of Mars 
has mainly been derived from a study of its surface at the 
very favorable oppositions, about 15 years apart, when the 
planet was near its perihelion, and consequently near its least 
distance of 34 million miles. Always at those times the 
inclination of the planet's axis brings the south pole into 
view, while the northern is turned from us. At the inter- 
mediate oppositions, when the planet's north pole is best 
visible, Mars is not far from aphelion, and least favorably situ- 
ate, in point of distance ; there is, however, a compensation in 
that the great telescopes of the world, located for the most part 
in northern latitudes, are better placed for observations of the 
planet. But its apparent diameter being so much reduced, and 
the difficulties of studying its surface so greatly augmented, rela- 
tively few observers have made a study of so unpromising an 
object as Mars on these occasions, when its distance usually 
exceeds 60 million miles ; and our knowledge of the northern 
hemisphere is proportionally incomplete. 

M r Knobel, among others, undertook to obliterate this in- 
equality during the opposition of 1884, and three of his sketches 
during that period are reproduced here. No irregularity in 



160 Stars and Telescopes 

the polar spot was detected. The next favorable oppositions 
for observing its north polar regions will occur in 1899, 1901, 
and 1903, when, with the planet's pole tilted toward the Earth, 
it is especially desirable that the phenomena of the melting of 
the northern polar cap be closely watched by experienced ob- 
servers with the most powerful telescopes. 

Curiously, while the north polar snows cap the exact pole 
quite concentrically, and as far as the 85th parallel of latitude 
all around, the south circumpolar snows do not centre about 
the pole, but round a point now nearly 200 miles removed from 




wth February wth February 10th February 

MARS AS DRAWN BY KNOBEL IN 1884 
{North polar cap near its greatest visibility) 

the planet's true pole, toward Mare Erythraeum. The well- 
established variation in the distance of the centre of the south 
cap from the true pole is unaccounted for ; it was as much as 
8° in the elder Herschei/s time (1783), and even 20 as 
measured by Linsser in 1862, but only 3 at the opposition in 
1892, according to Professor Comstock, whose observations 
very clearly bring out not only the rapid shrinking of the snow- 
cap — its diameter diminishing about fifteen miles daily — but a 
progressive shifting of its centre, which would seem to show an 
unsymmetrical shrinking. At the beginning of the Martian 
summer the polar cap reached down to latitude 70 , and its 
diameter was 1200 miles. In three months it had shrunk to 
one seventh this diameter. Probably the north cap was all the 
while increasing, but this pole was turned away from the Earth, 
and consequently invisible. 



The Ruddy Planet 161 

All the changing conditions of 1892 were most scrupulously 
observed by Professor Pickering, then located at the Harvard 
Observatory in the Andes of Peru (frontispiece), where, with 
a 13-inch telescope he had much better opportunity than any 
other astronomer for observing the planet at its nearest ap- 
proach to the Earth. Mars was faithfully followed on every 
night but one, from 13th July to 9th September, and the appar- 
ent alterations in the polar cap, even from night to night, were 
very marked. As the snow began to decrease, a long dark 
line made its appearance near the middle of the cap, and grad- 
ually grew until it cut the cap in two. This white polar area 
(and probably also the northern one), with the progress of its 
summer season becomes notched on its edge, dark interior 
spots and fissures form, isolated patches separate from the 
principal mass, and later seem to dissolve and disappear. It 
is much as if one were located at the distance of Mars and 
viewing with a telescope the effect of the advancing summer 
season upon the ice and snow of circumpolar regions of a 
nearly cloudless Earth. 

Evidently the fluctuations of the polar caps are the key to 
the physiographic situation on Mars, and at the opposition of 
1894, as well as that of 1892, the southern one has been criti- 
cally scrutinized. The south pole reached its maximum dip of 
24 toward the Earth on 22d June 1894. The rate of its pro- 
gressive diminution is by no means constant, and its area, some- 
times increasing and again diminishing, is at other times 
intersected by one or more dark narrow markings ; naturally 
interpreted as heavy falls of snow in the one case, and in the 
other as the melting of snow in the polar valleys. These fluctu- 
ations were subjected to exact measurement by M. Flammarion 
and others ; and the average rate of diminution was not very 
different from that found by Professor Comstock in 1892. One 
* great rift ' of the polar cap, very conspicuous, M r Lowell com- 
pared to the appearance of ' a huge cart-track coming down to 
one over the snow.' Its breadth he estimates at 220 miles, and 
length 1,200. Surrounding this polar cap is a narrow, dark 
line, nearly uniform in breadth, which is, M r Lowell surmises, 
' clearly water at the edge of the melting snow — a polar sea, in 
short.' Concerning the dark line dividing the polar cap, which 
made its appearance in the same place at the corresponding 
Martian season in 1894, he farther says: ' It started appar- 
ently not far from the centre of the snow-cap, and increased in 
width and length till it opened into the polar sea in longitude 
s& T — ir 



1 62 Stars mid Telescopes 

160 . Later its opposite end came out in longitude 330 . 
Meanwhile it was spreading even faster in the middle. While 
it was thus eating into the snow, some brilliant points, shining 
like stars, were observed in the snow between it and the outer 
edo-e of the cap on several successive mornings. They un- 
doubtedly were the far-off glisten of snow-slopes. The subse- 
quent behavior of the spots from which they came bore witness 
to this. For the rift grew till it formed a large lake in the 
midst of the snow not far from the geographical pole. Other 
rifts also appeared and ate into the cap, but the spots that had 
shone out so brilliantly still remained as snow islands, though 
daily diminished in size. At last the smaller of the two chief 
portions into which the cap had been split dwindled entirely 
away, and the other became a tiny patch eccentrically placed.' 
In consequence of the one-sided situation of the southern 
cap, the planet's true pole is always uncovered at the height of 
the summer season ; and until the opposition of 1894, the min- 
imum size of this cap was that observed by Schiaparelli in 
1879, wnen its diameter shrank to less than 150 miles. But 
the observers at Flagstaff were treated to a genuine surprise, 
when, in October 1894, M r Douglass witnessed the complete 
disappearance of this polar cap, undoubtedly the first phenome- 
non of this character ever recorded ; it was verified also by 
Professor Wilson at Northfield, M. Bigourdan of Paris, and 
others. The region formerly occupied by it became in no 
respect different from the east and west limbs of the planet. 

The Terminator 

As Mars is the nearest of the outer planets, its phase at 
times is very marked, being about like that of the Moon when 
two days before or after full. (See the illustration on page 
172). Its terminator, the line marking the limit of visibility on 
the incomplete side of the disk, may therefore be well observed ; 
and the phenomena of this region should tell us much about 
the general character of the planet's surface. 

Bright projections on the terminator of Mars were first ob- 
served by M r Knobel, who, on several occasions in 1873, 
described and delineated a white spot in this position, ' glisten- 
ing as brightly as the polar ice.' In 1884, however, with Mars 
at a corresponding phase, he could detect no bright spot in the 
same areographic location. Similar markings were discerned 
by M. Terby in 1890. Also, in August 1894, MM. Perrotin 




DWINDLING OF THE SOUTH POLAR CAP IN 1894 (LOWELL) 

{The planet 's pole of rotation is at the middle point of the square, and 
the eccentric position of the cap is shown, as well as the 
gradually diminishing breadth of the dark belt that fringed 
the Polar cap at all times) 



The Ruddy Planet 163 

and Javelle, and M r Williams saw brilliant projections be- 
yond the terminator, which, in case they are constant in posi- 
tion, are probably due to Martian mountains, or clouds, or a 
combination of both. Certain gray regions of large area, as 
watched by Professor Pickering in passing the terminator, 
were notched to different depths, indicating hills and valleys, 
and not the surface of an ocean. At the recent oppositions, 
irregularities of the Martian terminator have been carefully 
looked for, particularly at the Lowell Observatory, where, on 
30th June 1894, M r Douglass detected local nattenings in this 
line of demarcation, 20° to 40 in extent. M r Lowell finds 
them almost invariably upon that part of the terminator where 
the darker of the dark regions was then passing out of sight. 
These chord-like flattenings are still unaccounted for. Also 
there were projections and small notches, similar to those on 
the lunar terminator, though much less pronounced, and indi- 
cating mountains of perhaps 3,000 to 4,000 feet elevation. 
About two months later, Professor Pickering sketched a 
series of unusually marked elevations and depressions upon 
the terminator (page 172). Eventually data of this character 
will suffice for a map of approximate contours, but great care 
is necessary in distinguishing those projections which the 
observations of 1896-97 indicate as perhaps due to cloud. 

Evidently the most persistent scrutiny of this ever-changing 
line of sunrise and sunset can alone enlighten us as to config- 
urations of the Martian surface, which without doubt is rela- 
tively flat in comparison with the present rugged contour of 
Earth and Moon. Only when the crowding enigmas of the 
Moon have dissolved shall we be readv to pronounce upon 
Martian appearances with certainty. Particularly must the 
marked changes of lunar objects with the direction of their 
illumination be critically interrogated as an auxiliary key to the 
situation on Mars. The striking systems of lunar ' streaks' 
vanish utterly as our satellite recedes from the full : and this 
simple fact shows the danger of attaching too great significance 
to apparent phenomena of the Martian surface which may turn 
out to be mere phantom changes of illumination. 



The Lakes, or Oases 

It is the vast orange-tint area of the northern hemisphere, 
probably little diversified with hills and valleys, which the 



164 



Stars and Telescopes 



keen eye of Professor Pickering first dotted with numerous 
darkish regions of relatively small extent, and which are con- 
nected together by the complex system of canali, intersecting 
the northern Martian continents, as if the lines of a huge sys- 
tem of triangulation. If these dark spots are lakes, they are 
not permanent reservoirs, like terrestrial ones, as sometimes 
they wholly disappear. Also their apparent doubling, or gemi- 
nation from time to 
time is not un- 
known. M r Low- 
ell adduces excel- 
lent reasons for 
regarding them as 
oases in the vast 
Arean deserts, and 
their visibility as 
due to the growth 
of vegetation with 
the advance of 
spring. On pp. 176— 
77 are twelve charts 
of Mars, obtained 
by photographing 
a globe on which all 
the known features 
of the planet had 
been drawn by M r 
Lowell, through 
whose courtesy they are here presented. They give compre- 
hensively the important results of his recent studies of the 
planet, and show the striking system of the spots admirably. 

Lacus Phoenicis, one of the southernmost, on very fine nights 
with medium power, appears as a small spot, almost black and 
nearly round, resembling a shadow of a Jovian satellite near 
the middle of its transit. A little farther south is one of the 
best known regions of the planet, also a dark, oval, isolated spot, 
about 530 miles in its longest diameter, and formerly called very 
appropriately the ' Oculus/ or eye of Mars. First observed by 
Maedler in 1830, charted as Terby Sea on Green's map, it is 
now known as Solis Lacus, after Schiaparelli. As early as 
June 1890 this keen observer saw it divided into two distinct 
parts, and on 2d September 1894, the Lick telescope enabled 
M r Schaeberle to divide it into three regions, all separate 




MARS AS SEEN WITH THE 30-INCH TELESCOPE 
AT NICE, 2D JULY 1888 (PERROTIN) 



The R teddy Planet 



165 



and very dark. M r Douglass has still farther subdivided it 
(page 166). Schiaparelli has often seen a large part of the 
planet's disk, particularly near the polar regions, sprinkled with 
minute white spots, for example, in January 1882, the region be- 
tween Ganges and Iris ; and these phenomena, so important in, 
studying the physical constitution of the planet, are often within 
the reach of moderate telescopes. But the smallest of the true 
1 oases/ or dark spots, which are about 60 miles in diameter, 
are even more difficult to see than their intersecting * canals/ 
and both oases and canals have been observed to fluctuate to- 
gether in visibility, as if they were parts of one intimately con- 
nected system. 

The Martian 'Canals' 

Although faint markings of this character were first indi- 
cated on the map of Beer and Maedler (1840), and Dawes 
detected eight or ten of them in 1864, they are generally regarded 
as the original discovery of Schiaparelli during the remark- 
able opposition of 1877, when he made the first extended tri- 
angulation of the Martian surface, and mapped most of the 
canali known at the present time. Many observers fail utterly 
to detect these delicate markings ; others, practised in the ob- 
servation of them (M r Williams, for example, who verified 
nearly all of them in 1894), would call the plainer ones con- 
spicuous, and the average of them not difficult. But at least 
they require a steady atmosphere, and a perfect telescope with 
a trained eye behind it. Not even then are they always visible. 
Their appearance and degree of visibility are variable, often in 



PROBABLE DETAIL OF ' CANALS/ IF ARTIFICIAL 



periods of only a few days' duration. Seemingly capricious 
even the general law of this variation is not yet fully understood. 
Generally only a few of the canali are visible at once. Owing to 
the changing physical aspects, as to Mars's season and orbital 
position with reference to the Earth, under which they may be 



1 66 



Stars and Telescopes 



presented, given markings of this type may for a long time re- 
main invisible ; but nearness of the planet is not essential to their 
visibility, for they were seen at the remote opposition of 1896-7. 
If it is granted that the canali have an artificial origin, and 
were constructed for the very reasonable purpose of irrigation, 
one would naturally expect their minute structure to be some- 
what as shown schematically on the previous page ; straight and 
relatively narrow channels through the middle, intersected, at 
intervals more or less regular, by a multitude of short cross- 
channels, throughout their entire length. Indeed, says Schia- 
parelli, they very often look like gray bands deepest in inten- 
sity at the middle and shaded at the edges. Such a theory 
would obviate the necessity of supposing that the canali are 
really as wide as they look ; because at our great distance, the 











Em 




^^38 




P^ 


-; jfrSJ 


^k 




'gaB^k,-^ 


^3 


s*f! 


<*.'■ 


- J: 


-■ 


- *- 


SEpS- 








'"^issElS. 



THE 'SOLIS LACUS ' REGION OF MARS 
{As drawn by Douglass, gtk October 1894. Scale, 1 incJf=. 1200 miles) 



apparent width of a 'canal ' would simply be equal to the mean 
breadth of the system. Optically it is a question of resolva- 
bility which ought not to be beyond the power of the largest 
existing telescopes with a perfect atmosphere. 

Straight in their course and rarely deviating from a great 
circle, but very different in length (from 300 to 4,000 miles), 
they join one another at various angles like spokes in the 
hub of a wheel ; and intersect the great northern continent 



The Ruddy Planet 



167 



with a marvellous network of fine darkish stripes. M r Lowell 
describes their color as a bluish green, identical with that of 
the seas with which they connect. While each canale main- 
tains its own width throughout its entire length, the breadth of 
these markings is by no means uniform ; perhaps 20 miles for 
the narrowest, and ten times that amount for the broadest, of 
which the Nilosyrtis is probably the easiest of all to see. But 
although minor changes are suspected, and beginning to be 
made out, the canali form a permanent configuration of the 
Martian surface ; and every canale, as is apparent from M r 
Lowell's charts, page 176, connects at its ends with another 
marking of like character, or with darker ones, possibly seas. 

Preferably, however, they converge toward the small spots 
named lakes, or oases ; for example, seven canali con- 
verge in Lacus Phoe7iicis ) eight in Trivium Charontis, six in 
Lunae Lacus, and six in Is?nenius Lacus. About 50 of these 
dark spots, or lakes, are now known, including the recent addi- 
tions of Pickering and Lowell. Often the canals open out 
into an expanding trumpet-shaped region — e. g., mouth of 
Nilosyrtis named Syrtis Major, an area which exhibits sea- 
sonal changes, as if due to vegetation. Schiaparelli's criti- 
cal studies of these markings, and their changes of width and 
colors at the oppositions of Mars in 1882, 1884, and 1886, when 
the planet's northern pole was turned toward us, have led him 
to the simple and natural interpre- 
tation that the canali form a veritable 
hydrographic system, for distributing 
the liquid mass of the melting snows. 
Whether one views this marvellous 
and intricate system as a whole, or 
in some detached portion of high de- 
tail, as in the opposite sketch of the 
Solis Lacus region by M r Douglass, 
it is difficult to escape the conviction 
that the canali have, at least in part, 
been designed and executed with a 
definite end in view. 

A dozen of the canali became vis- 
ible to M r Lowell at Flagstaff in 
1894, ten weeks preceding the sum- 
mer solstice of Mars's southern hem- 
isphere ; and there were abundant verifications by many other 
astronomers in widely separate localities and with instruments 




MARS, 14th OCTOBER 1894 

(Brenner) 
( The elongated chain-link, 
region is the Mare Citn- 
merium) 



1 68 Stars and Telescopes 

of varying capacity, — Professor Wilson, Northfield, Minne- 
sota, and the Mount Hamilton observers, 30 canali by Herr 
Brenner in Istria, 40 by M. Antoniadi (who, at M. Flam- 
marion's observatory at Juvisy, made numerous fine sketches 
of Mars), and 50 by Mr Williams of Brighton, who saw nearly 
all those marked on Schiaparelli's map, and a few new ones 
in addition. But this record was far outstripped at the Lowell 
Observatory, where some of the canals appear on more than 
one hundred separate drawings, and 183 canals were seen in 
all. M r Lowell has made out a progressive change in the tint 
of the canali, which he regards as seasonal, and probably due 
to actual water, and vegetation fed by it. Naturally, extensive 
irrigation and agricultural operations on a large scale would 
seem the most likely explanation of the canali, especially when 
we reflect that upon Mars, doubtless a world farther advanced 
in its life history than our own, in the first place, erosion may 
have worn the continents down to a minimum elevation, making 
artificial water-ways easy to construct ; also with its vanishing 
atmosphere and absence of rains, the necessity of water for 
prolonging the support of animal and vegetable life could only " 
be met by conducting water from one part of the planet to 
another in channels artificial or partly so. 

In our present knowledge of the canali, this seems a plausible 
•explanation ; but many years of patient investigation are yet 
required, especially with larger telescopes on perfect mountain 
sites and by the most painstaking observers. Particularly 
are the best conditions for telescopic research paramount, be- 
cause the canali manifest themselves chiefly in the northern 
hemisphere of Mars. To ascertain the true significance of the 
-canali, however, does not necessarily seem to be forever beyond 
the power of man. The argument of the ' canals ' is fully pre- 
sented by M r Lowell in his interesting volume on Mars (Bos- 
ton 1895) > an d since its publication he has employed his 24-inch 
Clark telescope in the study of Mars during its opposition in 
1896-97. The north polar cap was first seen in August 1896, 
practically central over the planet's north pole, and covering a 
stretch of 50 in latitude, equivalent to 1800 miles. 

Seasonal changes are well illustrated in the colored plate 
(see Frontispiece), showing Hesperia central at three epochs 
months apart : in early spring the polar cap has just begun to 
shrink; in early summer canals are beginning to develop from 
south to north ; in late summer they are fully developed and 
the polar cap has vanished. 



170 Stars and Telescopes 



Doubling of the * Canals' 

Most striking of all the phenomena of Mars is the periodic 
doubling of the canali, also discovered by Schiaparelli, who 
first detected in 1879 the gemination of Nilus. Two years later 
this occurrence presented itself extensively, and he established it 
as a characteristic feature of the Arean continents. At about the 
Martian equinoxes, just before and after the apparent inunda- 
tion of the northern continent, occurs this surprising phenom- 
enon — never shown by all the canali simultaneously ; but under 
the proper seasonal conditions, the gemination makes its appear- 
ance irregularly and in isolated instances. A few of the canali 
even have never been seen doubled, of which the Nilosyrtis is 
one. The gemination takes place rapidly, in a few hours or 
days at the most ; and the original and previously single mark- 
ing becomes paralleled with precision by its duplicate, the dis- 
tances between the faint parallel lines being as small as 25 
miles in some cases, and ranging up to 350 miles in others. 
Reference is again made to M r Lowell's excellent charts, 
pp. 176-77, on which Ganges and Nectar (chart No. 3) are typi- 
cal instances of greatest and least distance between twin canals. 
Ordinarily the two bands appear equal, as well as parallel, and 
of the same color and intensity; but the gemination of course 
is not to be seen at all, except at suitable seasons, and even 
then it is visible only with difficulty. 

This strange transformation from single markings into double 
ones, was many years doubted by astronomers generally ; but 
having now been verified on many occasions, and independ- 
ently, by M. Terby, M r Williams, the Lick astronomers, and 
many other observers, it has been most reliably confirmed by 
M. Perrotin, formerly director of the great observatory on 
Mont Gros, depicted on page 169. One of his excellent 
sketches has already been given on page 164. The gemina- 
tions are found to vary at different recurrences, so that they 
cannot be fixed formations on Mars, as the canali themselves 
are. After some months of visibility, the twin marking fades 
out, and is seen no more till the favorable epoch again recurs. 
If Schiaparelli's theory is the true one, the duplication can 
occur only between the spring and autumn equinox of the 
northern hemisphere. A recent opportunity, thus, was in 
1890, and a later one occurred in January and February 1895 » 



The Ruddy Planet 



171 



but already M r Lowell, from his lofty station in Arizona, 
had on 19th November 1894 seen Phison and Euphrates 
double, and M r Williams in the same season had recorded 
the gemination of Ganges, Eunostos, Cerberus and others. 
Again the gemination duly put in an appearance in 1897, and 
was depicted in many drawings by M r Lowell. The width 
of each of the double canals was 25 to 40 miles, and their dis- 
tance apart 135 to 170 miles, from centre to centre. The 
oases were about 200 miles in diameter, and nearly all of them 
were seen to lie exactly between the twin canals. Among 
others who saw the double canals at this opposition was M. 
Cerulli, one of whose drawings is here given, showing the 




MARS, 17TH JANUARY 1897 (CERULLl) 
{The long double canal is Eumenides-Orcus) 



Eumenides-Orcus plainly double. It is somewhat curious that 
those observers who have seen the gemination best are most 
puzzled as to the cause of it. In fact, no plausible explanation 
of this wonderful phenomenon has yet been advanced, although 
many crude guesses have been hazarded. M. Antoniadi has 
sought to account for it by maladjustment of focus. That it 
cannot be due to optical illusion or double refraction seems 
quite certain; rather the twin canal appears to have in each 
case a real existence. 

The sketch on page 172 shows a portion of Mars not com- 
monly drawn, which with ordinary seeing affords scarcely any 
detail, except mere outlines. At the same time a number of 
the more interesting and difficult features are shown. Descrip- 



172 



Stars and Telescopes 




MARS AS SEEN AT THE LOWELL OBSERVATORY, ARIZONA 
16th August 1894, under fine atmospheric conditions {by Professor W. H. Pickering, with 
the 18-inch Brashear telescope, -magnifying power 420) 

The scale is 73.-stys.7nn7 > that is, 1 millimetre — 73.5 kilometres •= 45! miles. The linear value 
of 1 second [of arc) is 6 -millimetres — \ inch {nearly). The two left hand ' * lakes, 1 connected by 
a nearly vertical ' canal ' 280 ;«/&$ long, are 1 second apart. The phase of Mars is near its 
greatest value. The arrow below indicates the direction of motion in consequence of the 
plane fs rotation. A bove and below the disk are two hair lines marking the position of the 
planet 1 s axis, which passes through the upper or south polar cap, whose displacement from 
the true pole is well shown. Into the seemingly minute area of one of the nearly central dark 
spots, or * lakes, 1 could be crowded 30 cities the size of New York. 



The Ruddy Planet 173 

tive of this drawing, Professor Pickering says, ' Syrtis Minor 
has nearly reached the middle of the disk, and Syrtis Major has 
just come around the limb. . . . The southern [upper] snow cap 
is bounded by a uniform black line, of the width shown in the 
sketch, and presumably due to water. Near it is a small iso- 
lated patch of snow, probably located upon a mountain range. 
. . . On the terminator is noticed a projection which is unusually 
high, and has unusually steep ends. Near the centre of the disk 
are seen six lakes and three canals. They are all difficult ob- 
jects. The diameter of the lakes was about o."i [36 miles], and 
the breadth of the canals oZ'05 [18 miles]. These canals are 
rather blacker than they should have been, and the southern 
lake is rather too conspicuous. In the northern hemisphere 
are seen the hazy, radiating surfaces which probably precede 
the formation of the canals. South of the northern cloud the 
dark regions were brownish, north of it, gray; while the Syrtis 
Major region was greenish gray. The northern hemisphere 
and the limb were yellow, the radiating bands very faint gray, 
and the extreme north bounded by the canal and the fine line, 
light green/ 

Still, great as is the amplification in this drawing, it will help 
to present in a forcible manner the difficulties with which 
astronomers must contend, if it is remembered that the area of 
the full Moon's apparent disk is 4000-fold that of the little 
■disk of Mars at his nearest. 

Martian Atmosphere 

Likelihood of an atmosphere encircling Mars is inferred from 
temporary obscurations of well-known and permanent mark- 
ings of the planet's surface, frequently observed and satisfac- 
torily attributed to clouds. An important occurrence of this 
character was recorded by M r Douglass, 24th September 1894, 
when the western half of Elysium appeared as if veiled for a 
time by a cloud, subsequently dissipated. Also M r Williams 
saw Mare Cimmerium itself occluded, with considerable varia- 
tions in the extent of the cloud envelope from day to day. In 
October 1894, the same careful observer saw what he considered 
to be cloud, or mist, affecting the visibility of the extensive 
land region north of Mare Cimmerium ; and he thinks these 
atmospheric occlusions are common and extensive. Mars, how- 
ever, seems never to be covered, as the Earth generally is, with 
vast cloud areas obliterating its continents and oceanic features, 



174 Stars and Telescopes 

but his skies appear to be nearly perpetually clear, in every 
climate and every zone. Now and then a few whitish spots, 
changing their form and position, though rarely extending over 
a very wide area, frequent the islands of Mare Australe, and 
Elysium and Tempe of the northern continents. Their varia- 
tion during the Martian day is well known, and Schiaparelli 
thinks them a thin veil of fog rather than a true nimbus of the 
type yielding terrestrial rains ; or possibly a temporary conden- 
sation of vapor as dew or hoar frost. 

The spectroscope, in the hands of Secchi, Huggins, Ruth- 
erfurd, Vogel, and Maunder, has given certain evidence 
of absorption lines in the spectrum of Mars not due to our own 
atmosphere ; and the inference has always been irresistible that 
the ruddy planet is surrounded by a gaseous envelope. D r 
Huggins in 1867 detected lines in the spectrum due to the 
presence of watery vapor ; also in the same year, embracing an 
opportunity when Mars and the Moon were at the same altitude, 
he found the spectra of the two bodies practically identical,, 
while, on applying photography in 1879 , no lines or modifica- 
tions peculiar to the planet's spectrum made their appearance. 
Professor Campbell, in July 1894, when Mars and the Moon- 
were again near together, repeated the observation of D r 
Huggins by making direct and critical comparison of their 
spectra under improved conditions of drier atmosphere and 
more powerful apparatus, with the identical result that the two- 
spectra were alike in every particular. This may be interpreted 
as meaning, of course, that Mars has no more atmosphere than 
the Moon itself, long known to be devoid of such an envelope. 

But the obstacles to such interpretation are by no means 
slight. For example, as the planet turns on its axis, carrying 
the spots from centre to edge of the disk, they gradually melt 
from view, just as they would if seen through a greater thick- 
ness of atmosphere. The temporary obscurations of certain 
parts of the disk, supposably by clouds, will have to be other- 
wise accounted for. The amount of water, too, must be inap- 
preciable, let alone the difficulties of explaining that periodic 
and well-established expansion and shrinking of the polar caps r 
if there is no atmosphere to act as a medium in the formation 
and deposition of snow. Professor Campbell does not con- 
sider the spectroscopic observations as proving that Mars has 
no atmosphere whatever, similar to our own, but simply that 
they set a superior limit to its extent. In the latter part of 
1894, both D r Huggins and D r Vogel repeated their examina- 



The Ruddy Planet 175 

tion of the spectrum of Mars, resulting in essential verification 
of their earlier researches ; and Professor Keeler, in the win- 
ter of 1896-97, obtained photographic tests at Allegheny which, 
as far as they go, agree with the visual results of Professor 
Campbell. But judgment upon the spectroscopic evidence of 
a Martian atmosphere must be suspended until the planet is 
again very favorably placed for observation in 1907. Mean- 
while, photometric observations by D r Muller show that the 
behavior of Mars, as to its phases, distinctly indicates an 
atmosphere comparable in density with that of the Earth. Also 
M r Lowell, in discussing a fine series of observations of the 
diameter of Mars, made at his observatory by M r Douglass in 
1894, finds an unmistakable twilight arc of 13 , — independent 
evidence of an atmosphere. The dimensions of Mars are 
4184 miles for the polar diameter, and 4206 for the equatorial, 
the polar compression of the planet being ^Jo- l^ r Schur, 
however, in 1896-7 finds it as great as -£ Y with the heliometer. 

In considering the possibility of an atmospheric envelope 
surrounding our neighbor planet, a few fundamental facts 
ought to be kept in clear and constant view. Mars is a planet 
intermediate in size between Moon and Earth : twice the diame- 
ter of the Moon equals the diameter of Mars ; and twice the 
diameter of Mars approximately equals the diameter of the 
Earth. As to masses the Moon is -fe, and Mars about \, the 
mass of our globe. We have here an abundant atmosphere : 
the Moon has none ; so it would seem safe to infer that 
Mars may have an atmosphere of slight density, -r- not dense 
enough for the spectroscope to detect, but dense enough to ac- 
count for the observed phenomena of the Martian disk, other- 
wise hard to explain. Indeed, Mattieu Williams, from 
considerations of the relative size and mass of the Earth and 
Mars, calculated that the ruddy planet is entitled to ^ the 
atmosphere that our globe has, and that the mercurial barome- 
ter would stand at about 5^ inches at the sea level on Mars. 

The climate of Mars, then, would seem likely to resemble 
that of a clear season on a very high terrestrial mountain, a 
climate of extremes, with great changes of temperature from day 
to night. But safe speculation regarding the possibility of or- 
ganic life upon the ruddy planet really hinges upon the selective 
absorption of the Martian atmosphere, and whether it aids the 
planet, as our atmosphere does, in storing heat by prevent- 
ing its radiation. And until it has become known whether the 
Earth's surface has yet reached, or has passed, that maximum 



176 Stars and Telescopes 

of secular temperature, toward which it must tend so long as it 
continues to receive more heat from the Sun than it radiates, 
obviously there is little use in speculating whether some other 
planet may or may not have passed that critical epoch. The 
inequality of Martian seasons is such that in the northern 
hemisphere, the cold season lasts 381 days, and the hot only 
306. The polar caps attain their maxima three or four months 
after the winter solstice, and their minima about the same time 
after the summer solstice ; and this lagging affords a strong 
argument for a Martian atmosphere with heat-storing properties 
similar to the Earth's. 

It should be observed that the existence of fluid water upon 
Mars would imply that the temperature of Arean climates is 
comparable with our own. The relations of the planet's axis 
to its orbit are similar to ours; but the supply of direct solar 
heat is about one-half as great per square mile as that of the 
Earth. Owing to the eccentricity of Mars's path round the 
Sun, the surface of the planet receives at perihelion about one- 
half more of solar heat than at aphelion; so that the southern 
summers must be much hotter and the winters colder than 
those of the northern hemisphere. The length of summer, 
twice that of the terrestrial season, may amply suffice to melt 
all the ice and snow, an unusual condition of things which 
actually took place in October 1894. 

But the aspect of the entire situation is somewhat modified 
by a recent paper (1898) by D r Johnstone Stoney of Dublin, 
whose investigations of the phenomena of planetary atmos- 
pheres began about 35 years ago. His method is based on 
the kinetic theory of gas ; according to which, if free molecules 
travel outward, as they often must, with velocities exceeding 
the limit that a planet's gravity can control, they will effect a 
permanent escape, forever after travelling in orbits of their own. 
So D r Stoney succeeds in accounting for the practically entire 
absence of atmosphere from the Moon, and of free hydrogen 
and helium from the Earth's encircling medium. Applying 
the same theory to Mars, he is led to the significant inference 
that water cannot in any of its forms remain upon that planet. 
Without water, there can of course be no vegetation such as 
we know; and in its absence much free oxygen is unlikely. 
Under these circumstances, analogy to the Earth suggests to 
him that the atmosphere of Mars consists mainly of nitrogen, 
argon and carbon dioxide. 

It is part of the province of physical science not only to 




i2o° — Nodus Gordii 



150° — Mare Sirenum 
THE PLANET MARS IN 



{At every 30 of Martian longitude, and 
earthward. Below each presentation is 
together with the name of the most prominent 




i8o° — Atlantis 



2io° — Trivium Charontis 




300 — Syrtis Major 

NOVEMBER 1894 (LOWELL) 

with the plane? s south (upper) pole tilted 23° 
given the longitude of the central meridian, 
marking upon it) 



330 — Phison and Euphrates 



The Ruddy Planet 



177 



observe and record, but to explain, natural phenomena. How 
then shall we explain the observed and regular fluctuations of 
polar caps, and the seasonal development of canals and oases ? 
As the hypothesis of water affords the readiest and most natu- 
ral explanation, we are driven to the important conclusion that 
the secular dissipation of water on Mars, while constantly pro- 
gressing through countless ages, is not yet complete, although 
his original store of water already exhibits marked signs of 
approaching exhaustion. 

From the motions of Earth and Mars given in previous chap- 
ters, it is easily found that the ruddy planet goes 17 times round 
the Sun in 32 years, or, more accurately, 25 times in 47 years. 
These relations then indicate when Mars may be best observed 
in the future, as the following table shows, in addition to those 
epochs of the past half century when this planet was excep- 
tionally well placed for observation : — 

Favorable Times for Observing Mars 



Years 


Mars nearest 
the Sun on 


Least Distance of Mars from 
the Earth 


Angular 
Diame- 
ter 


Declina- 
tion of 
Mars 


Average 

Meridian 

Altitude 

in the U.S. 


On 


In miles 


1845 
i860 
1862 

1877 
1892 
1894 
1907 
1909 


August 30 
Sept. 16 
August 4 
August 21 
Sept. 7 
July 26 
Sept. 24 
August 13 


August 18 
July 22 
Sept. 29 
Sept. 2 
August 6 
Oct. 13 
July 12 
Sept. 20 


34,610,000 
36,270,000 
37,660,000 
34,950,000 
35,020,000 
40,000,000 

39,000,000 
36,000,000 


SO" 

29 
28 

30 
29 
26 

27 
29 


20°S. 

27 S. 
2 N. 
12 S. 

24 s. 
9 N. 
20 S. 

4 s. 


28° 
21 

3 6 
24 

57 
28 

44 



All delicate questions concerning the planet's surface, its 
southern hemisphere in particular, must now be tabled for 
many years. Meanwhile, the northern regions are being faith- 
fully interrogated as they come more and more within reach ; and 
the intervening years will afford opportunity for thoroughly 
discussing all the earlier drawings, and, in the light of large 
and freshly garnered harvests, welding them together into a 
homogeneous system, capable of consistent and reasonable 
interpretation. 



s&T— -12 



178 Stars and Telescopes 

In additon to the references for this planet already given on 
page 147, consult first of all Flammarion's comprehensive work 
entitled La Planete Mars etses conditions d'habitabilite : synthase 
generate de tontes tes observations (Paris 1S92). Also the follow- 
ing, comprising the bulk of the more important Martian liter- 
ature, both popular and technical, chiefly since 1885: — 

Williams, ' Meteorology,' Fuel of the Sun (London 1870). 
Green, At Madeira in 1877, Mem. R. A. S. xliv. (1879), I2 3- 
Hartwig, ' Diameter/ Pud/. Astron. Gesell. xv. (Leipzig 1S79). 
Young, 'Diameter,' Am. Jour. Sci. cxix. (1880), 206. 
Schroter, Areographische Beitrage (Leiden 1S81). 
Maunder, The Sunday Magazine, xi. (1882), 30, 102, 170. 
Trouvelot, Comptes Rendus, xcviii. (1S84), 788 ; L' Astronomic 

iii. (1884), 321 ; Observatory, vii. (1884), 369. 
Bakhuyzen, 'Rotation,' Ann. Sternwarte Leiden, vii. (1S85). 
Green, ' Northern hemisphere,' M. A 7 ". R. A. S. xlvi. (1S86), 445. 
Perrotin, * Les Canaux,' Bulletin Astron. iii. (1SS6), 324. 
Stanislas Meunier, Pop. Sci. Monthly, xxxi. (1SS7), 532. 
Fizeau, Janssen, Perrotin, Terby, Co/up. Rend. cvi. (iSSS). 
Flammarion, Perrotin, Comptes Reudus, cvii. (1SS8). 
Maunder, 'Canals,' The Observatory, xi. (18S8), 345. 
Niestex, Bulletins Acad. Roy. Belgique, xvi. (iSSS), N* 7. 
Flammarion, 'Variations,' Bull. Soc. Astron. de France (18SS). 
Perrotin, 'Canals,' V Astronomic, vii. (1S8S), 366. 
Terby, Cielet Terre, ix. (1S8S), 271, 289 ; xii. (1891) ; Memoires 

couronnes Acad. Belgique (188S); Bull. Acad. Belgique, xx. 

(1S90) ; V Astronomic, ix. (1S90). 
Wilson, ■ Canals,' Sidereal Messenger, viii. (1SS9), 13. 
Gerigny, ' Les Marees,' V Astronomic, viii. (1889), 381. 
Young, The Presbyterian Review, x. (1889), 400. 
Hall, Holden, The Astronomical Journal, viii. (1889), 79, 97. 
Schiaparelli, V Astronomic, viii. (18S9), 19, 42, 89, 124; 

Himmel und Erde, i. (18S9), 1, 85, 147. 
Meisel, Astronomische Nackrichten, exxi. (1889), 371. 
Scheiner. ib. exxii. (1889), 251. 

Wislicenus, ib. cxx. (18S9), 241 ; exxvii. (1891), 161. 
Pickering, ' Photographs,' Sid. Mess. ix. (1890), 254, 369. 
Ritchie, ib. ix. (1890), 450. 
Williams, A. S., ' Canals and markings,' Jour. Brit. Astron. 

Association, i. (1890), 82. 
Flammarion, L'Astrono??iie,x. (1891), xi. (1892). 
Lohse, Pnbl. Astrophys. Observatorium Potsdam, N r 28 (1891). 



The Ruddy Planet 179 

Lohse, Maunder, Niesten, Jour. Brit. Astron. Association, 

ii. (1892), 417, 423, 5°7- 
Tisserand, 'Diameter,' Bulletin Astronomique, ix. (1892), 417. 
Flammarion, Perrotin, Meunier, Comp. Rend. cxv. (1892). 
Lockyer, J. N., A T ature, xlvi. (1892), 443. 
Barnard, Comstock, Pickering, Terby, Wilson, Young, 

Astronomy and Astro-Physics, xi. (1892). 
Flammarion, Lockyer, Pickering, Nature, xlvii. (1892). 
Ball, /;/ Starry Realms (London 1892), chapter xii. 
Ball, The Fortnightly Review, lii. (1892), 288; In the High 

Heave?is (London 1893), chapter vi. 
Peal, ' Distribution of land and water/ Jour. Brit. Astron. 

Association, iii. (1893), 22 3* 
Comstock, * South Polar Cap,' Astron. Jour. xiii. (1893), 4 1 - 
Keeler, Memoirs Royal Astronomical Society, li. (1893), 45- 
Abetti, ' South Polar Spot/ Astron. Nachr. cxxxiii. (1893), 2 5- 
Maunder, Jour. Brit. Astron. Association, iv. (1894), 395. 
Douglass, Lowell, Pickering, Schaeberle, Schiaparelli, 

and others, Astronomy and Astro- Physics, xiii. (1894). 
Flammarion, V A stronomie, xiii. (1894), 447. 
Lowell, Popular Astrojwmy, ii. (1894). 
Meyer, Die Physische Beschaffenheit (Berlin 1894). 
Campbell, ' Atmosphere/ Publ. Astron. Society Pacific, vi. 

(1894), 228, 273. 
Antoniadi, Lowell, Nature, li. (1894), 40, 64, 87, 259. 
Huggins, Knobel, Williams, The Observatory, xvii. (1894). 
Lockyer, W. J., Nature, 1. (1894), 476, 499. 
Young, 'Diameter/ The Astronomical Journal, xiv. (1895), x ^5* 
Brenner, Sketches 1894, Astron. Nachr. cxxxvii. (1895), 49- 
Ellery, The A strophysical Journal, i. (1895), 47* 
Lowell, Mars (Boston 1895). 
Schiaparelli, Osservazioni astronomiche e fisiche sulV asse di 

rotazione et sulla topograjia del pianeta Marte (Rome 1897). 

Also 4 previous memoirs by same author. 
Perrotin, 'Zones/ The Observatory, xx. (1897), 132. 
Brenner, Abhandl. Kon. Akad. Wiss. Berlin, 1897. 
Lohse, Publ. Astrophys. Observatorium Potsdam, xi. (1898). 
Stoney, 'Atmosphere/ Astrophys. Jour. vii. (1898), 44. 
Cerulli, Marte nel 1896-97 (Collurania 1898). 
Lowell, Annals Lowell Observatory, i. (Boston 1898). 

Bibliographic lists in the ' Smithsonian Report ' each year 
comprise many additional titles. For papers since 1895 consult 
the bibliographies in The A strophysical Journal. 



180 Stars and Telescopes 



The Plurality of Worlds, etc. 

The absorbing popular interest of this subject, and the serious 
attention accorded it by many eminent writers, render a brief 
list of the better literature worthy of the space here given it. 

Huygens, Cosmotheoros (Opera, ii. p. 641) (1755). 

Fontenelle, Entretiens sur la Pluralite des Monde s (Paris 
1852) ; with notes by Proctor, Knowledge^ vi. (1884); Y ^> 
(1885). 

Whewell, The Plurality of Worlds (London 1853). 

Brewster, More Worlds than One (London 1855). 

Smith, H. J. S., Oxford Essays (1855), 105. 

Flammarion, La Pluralite des Mondes habites (Paris 1863). 

Proctor, Other Worlds tha7i Ours (London 1870). 

Searle, G. M., The Catholic World, xxxvii. (1883), 49; lv. 
(1892), 860. 

Miller, W., The Heaveiily Bodies (London 1883). 

Proctor, ' Life in Other Worlds,' Knowledge, vii. (1885). 

Burr, ' Are heavens inhabited ? ' Presby. Rev. vi. (1885), 257. 

Porter, 0?cr Celestial Home (New York 18S8). 

Searle, G. M., Pub. Astron. Society Pacific, ii. (1890), 165. 

Flammarion, U Astronomie, x. (1891). 

Guillemin, ' Communication with the planets/ Popular Sci- 
ence Monthly, xl. (1892), 361. 

Ball, 'Life in other worlds/ The Fortnightly Review, lvL 
(1894), 718; McClure's Magazine, v. (1895), *47- 

Flammarion, No. Am. Rev. clxii. (1896), 546. 

Janssen, Popular Science Monthly, 1. (1896), 812. 

Serviss, ib. lii. (1897), 171. 

For the periodical literature, much of it worthless, consult 
under Worlds, the indexes of Poole and Fletcher, often 
cited ; also, Matson's References for Literary Workers (Chicago 
1892) contains, at pp. 410-412, abundant references to papers 
on the plurality of worlds, an interminable subject. 



CHAPTER XII 

COMETS 

TI7HEN Kepler had shown that the planetary 
* * orbits are ellipses, and Newton had proved 
that this is a necessary consequence of their being 
attracted toward the Sun with a force varying in- 
versely as the square of the distance from him, it was 
natural to surmise that comets also might be moving 
round the Sun, in ellipses so much more eccentric 
that these bodies would be visible only in those parts 
of their elongated orbits which are nearest to the Sun 
and Earth. As the law of equable description of areas 
would of course hold good in their case, causing them 
while in these nearer parts of their courses to move 
much more rapidly than in any other part, the comets 
would obviously be visible during only a small portion 
of their whole orbital revolution. 

Newton applied these principles to the splendid 
comet of 1680 (visible a few years before the publi- 
cation of the first edition of the Principia in 1687), 
and found that it was moving in an ellipse of so 
eccentric a character as to approach very nearly in 
form to a parabola. It was thought by himself and 
by Halley that it might be identical with great 
comets recorded as having been seen in b. c. 44, a. d. 
531, and a. d. 1 106, and that the period was about 
575 years in length. Subsequent investigations have 
not confirmed this particular conjecture, and it is 



182 



Stars and Telescopes 



probable that the actual period of that remarkable 
comet (which made such an exceptionally close 
approach to the Sun) amounts to, not hundreds, but 
thousands of years ; so that any previous appearances 
most likely took place before historic dates. But in 
regard to a fine comet which appeared two years 
later, in 1682, Halley was able, after calculating the 
elements of its orbit, to show that 
they were almost precisely the same 
as those of comets observed in 1531 
and 1607, so far at least as could be 
decided by the observations accessible 
to him. Hence in this case there was 
ground for concluding that all these 
appearances were one and the same 
comet ; that its period was about 75 
or 76 years in duration, and that it 
would probably return in 1758 or 
1759. It did so return, being first 
seen by Palitzsch, near Dresden, on 
Christmas Day, 1758; and it has 
ever since been known by the name 
of the illustrious astronomer who had so confidently 
predicted its return. It passed its perihelion at that 
appearance, 12th March 1759, and at the next return, 
1 6th November 1835. According to Pontecoulant, 
it will be due at perihelion again in 19 10. The dis- 
tance of Halley's comet from the Sun varies between 
0.58 and 35.3, in terms of the Earth's mean distance ; 
that of Venus, expressed in the same way, being 0.72, 
and of Neptune, 30.05. 

A very large proportion of the known comets travel 
in parabolas, or in ellipses of such great eccentricity 
as to be undistinguishable from parabolas during the 




halley's comet 

IN 1835 
(Struve) 



Comets 



183 



time of visibility. 89 Following are a few particulars 
about the most remarkable comets which are moving 
in elliptical orbits of moderate eccentricity. 

39 The trustworthy records of cometary apparitions through 
out all past time are about 1000 in number, and the increase is 
very rapid at the present day, because many skilful observers 
with suitable telescopes are continually searching for comets. 
Nearly one half of the entire number (rather more than 400) 
have been subjected to mathematical calculation, and the paths 
of their motion determined. It is only by the agreement among 
the elements of these paths that the identity of two or more 
comets can be proved ; for the physical appearance and charac- 
teristics of a given comet are generally very different at the 
different returns. When a comet is first discovered, if remote 
from the Sun, its appearance will usually resemble that of the 
Pons-Brooks comet (page 188, left) ; and a large proportion of 
telescopic comets never develop beyond this simple stage. But, 
if the comet is a great one, on approaching nearer a nucleus 
will begin to aggregate in that part of the hazy mass on the 
farther side from the Sun ; from this centre the wonderful phe- 
nomena of the coma, or head, soon manifest themselves, un- 
folding in envelopes or sheaths, as in Coggia's comet of 1874 
(page 205), or more often opening toward the Sun, like the 




THE GREAT COMET OF l86l 
(WILLIAMS) 



HEAD OF THE GREAT COMET OF l86l 
HIGHLY MAGNIFIED (sECCHl) 

{The tail is directed downward) 



separate parts of a fan, the handle of which is at the nucleus 
of the comet. This structure is well shown in the adjacent 



184 



Stars and Telescopes 



Of the periodic comets, Halley's, by far the most 
interesting, has been traced with high probability for 

illustration of the head of the great comet of 1861. (A general 
view of the entire object, as it appeared in the northern heav- 
ens, is given above in miniature. This remarkable body, dis- 
covered 13th May 1861 by M r Tebbutt of New South Wales, 
had a tail which appeared to stretch one third the way round 
the heavens. The Earth and Moon passed through the tail 
of this body, 30th June 1861, with no apparent effect save a 
peculiar sky glare. According to Sir John Herschel, this 
comet far exceeded in brilliancy all other comets that he had 
ever seen, even those of 181 1 and 1858. It recedes from the 
Sun to a distance nearly twice that of Neptune, in an elliptical 
orbit, with a period of 410 years.) On the side of the nucleus 

opposite the fan, and almost in- 
variably directed away from the 
Sun, begins the development of 
the tail of the comet, usually the 
most striking characteristic of a 
great comet. Cometary tails some- 
times appear almost straight, and 
'others have varying degrees of 
curvature. A typical tail is that 
of Brooks's comet (1886 V), 
shown in the accompanying illus- 
tration. Other comets (for ex- 
ample, Donati's, the sixth comet 
of 1858, shown on page 203) have 
tails both straight and curved. 
When a comet has passed its 
perihelion, the tail will, in nearly 
all cases, be found to have swung 
round and changed its apparent 
position with respect to the comet's 
motion ; so that it will still remain 
true that the tail is directed from 
the Sun, and the comet will move away from the Sun with its 
head following the tail. The early astronomers described the 
tail in this position as the ' beard.' Generally the median line 
of the tail of a large comet is dark ; though this sometimes 
changes to a brighter streak, and vice versa, as in the case of 
Coggia's comet of 1874. 




brooks's comet (1886 v; 

{7th May 1886) 



Comets 185 

nearly 1900 years. Dion Cassius tells us of a comet 
seen in b. c. 12, about the time of the death of the 

The tails of comets appear to be made up from the material 
particles first projected toward the Sun from the nucleus in a 
manner incompletely understood ; afterward curving over and 
forming the cup-shaped sheaths of the coma, and then repelled 
by the Sun to form the trains of various types. It seems likely 
that these filmy, evanescent objects exist as hollow cones in 
space. Bessel in Germany, Norton in America, and in par- 
ticular Bredichin in Russia, have contributed most to estab- 
lish a theory of comets' tails which accounts for nearly all the 
facts of observation. Bredichin's theory is that the straight 
tails, like those of the comets of 1858 and 1861, are probably 
composed of hydrogen, the Sun's action of repulsion upon 
which would exceed twelve times the attraction of gravitation; 
the moderately curved tails (the usual type) are hydrocarbons 
in gaseous forms, with an action of repulsion slightly in excess 
of gravity along the inner edge of the tail, and increasing to 2% 
times that amount on the outer edge ; and a few comets exhibit 
still a third type of tail, — short, sharply curved, probably due 
to the vapor of heavier substances (iron, chlorine, and sodium), 
upon which the repulsive effect is relatively weak, varying be- 
tween yV an d \ that of the Sun's gravitative action. In rare 
instances a comet has been known to exhibit tails of all three 
of these types. Probably the tail of a comet is formed by an 
expenditure of the substances composing the nucleus, in such 
a manner that the particles once leaving the nucleus are never 
returned to it. The larger comets, then, must grow smaller 
and smaller at every return to perihelion. Undoubtedly this is 
the true explanation of the faint and tailless condition of most 
of the short period comets, whose encounters with solar dis- 
rupting influences have been frequent. 

The visibility of comets chiefly depends upon two condi- 
tions, — their intrinsic lustre, and their position in space rela- 
tively to Sun and Earth. While some are seen for a few days 
only, and the average visibility is about three months in dura- 
tion, on rare occasions a comet can be observed throughout an 
entire year, and the great comet of 181 1 was visible for 17 
months. In nearly all cases, the curve traversed during visi- 
bility is only a small part of the entire path, so that a degree 
of uncertainty exists in cometary orbits which does not obtain 
in determining the paths of planets. — D. P. T. 



1 86 Stars and Telescopes 

great Roman general Agrippa, and the Chinese annals 
also mention a comet seen at a date corresponding to 
this. D r Hind has shown that this was probably the 
first appearance of Halley's comet. It is also prob- 
ably referred to by Josephus as seen in a. d. 66, when 
the Jewish rebellion broke out which led to the de- 
struction of Jerusalem four years afterward by the 
Roman army under Titus. The Chinese records also 
speak of a comet seen at that time, as well as of 
another in a. d. 141, which was probably the same. 
In a. d. 218 it appears to have been noticed both in 
China and Europe, being followed (according to Dion 
Cassius) by the death of Opilius Macrinus, the Em- 
peror, soon after his defeat at Irumae, near Antioch, 
by Elagabalus. In the years 295 and 373 we are 
also able to recognize with much probability Halley's 
comet in accounts furnished by Chinese annalists ; 
and it can hardly be doubted that this comet was seen 
in a. d. 451, not only in China, but also in Europe 
(about the time of the great defeat of the Huns under 
Attila near Chalons-sur-Marne by iEnus and Theo- 
doric). In a. d. 530 or 531, during the reign of 
Justinl^n, < a very large and fearful comet ' was seen, 
which (as already mentioned) Newton and Halley 
thought to be an appearance of the comet of 1680. 
The fuller observations of the Chinese have become 
accessible to us since their time, and show that it 
was more likely the comet of 1682. 40 

40 * Ugly monsters ' that comets always were to the ancient 
world, the mediaeval church perpetuated the misconception 
with such vigor that even yet these gauzy, harmless visitors from 
the interstellar spaces have a certain * wizard hold upon our 
imagination/ This entertaining phase of the subject is invitingly 
treated in President Andrew D. White's scholarly * History 
of the Doctrine of Comets ' (Papers of the American Historical 



Comets 187 

Like some previous appearances, the returns of 
a. d. 608 and 684 were, so far as is known, recorded 
only in the Chinese annals \ but in a. d. 760 a re- 
markable comet was chronicled, not only by their 
annalists but by a Byzantine historian in the reign 
of Constantine Copronymus, and D r Hind thinks it 
little short of a certainty that this too was a return 
of Halley's comet. Also, appearances of it were 
probably seen both in Europe and China in a. d. 837 
and 912; likewise in a. d. 989, as related in the 
Chinese records only. The next return was in the 
year of the Norman Conquest. On the Bayeux 
tapestry there is a representation of some people gaz- 
ing at a comet which appeared soon after Easter 
a. d. 1066, while England was threatened with two 
invasions at once, — both taking place in succession, 
but with very different terminations. This comet also 
was doubtless Halley's, and it was seen again in 1145, 
1223, 1 30 1, 1378, and 1456. In the latter year it 
seems to have been very conspicuous, making a great 
sensation in Europe, where the Turks, who had taken 
Constantinople only three years previously, were ad- 
vancing into Hungary, when they were defeated and 
repulsed at Belgrade by the famous Hunyadi. At the 
succeeding return in 153 1, the comet was apparently 
less brilliant ; at any rate our knowledge of its path on 
that occasion depends entirely upon the observations 
of Peter Apian, or Bienewitz. In 1607 this comet 

Association, vol. ii.) ; while for a very extensive collection of 
the literature of comets, both historical and scientific, reference 
may be had to the Catalogue of the Crawford Library of the 
Royal Observatory, Edinburgh (1890), pp. 89-142. The titles 
of many other important papers and treatises on comets are 
given at the end of this chapter. — D. P. T. 



i88 



Stars and Telescopes 



was observed by the illustrious Kepler ; and it was by 
a comparison of elements principally deduced from 
his observations in that year, and Apian's in 1531, that 
Halley identified these comets with the one ob- 
served by himself in 1682. 

Two other comets have periods a little shorter than 
Halley's, but their history cannot be traced farther 
back than the apparitions preceding the last. One 
of them, found at Marseilles, 20th July 181 2, by Pons, 
the most successful of all discoverers of comets, be- 
came visible for a few days to the naked eye, and 





PONS-BROOKS COMET, 26th OCTO- 
BER 1883 

(A typical telescopic comet ; nucleus ill 
defined, coma undeveloped, tailless) 



( PONS-BROOKS COMET) 

{Drawn by D>' Swift 
2gtn December 1883) 



passed its perihelion on 15 th September, the very day 
on which the conflagration of Moscow broke out dur- 
ing the French occupation of that city under Napo- 
leon. Encke's calculations made its period 70* 
years. Rediscovered by M r Brooks at Phelps, New 
York, 1 st September 1883, renewed observations 
showed that the period was slightly longer, and that 



Comets 



189 



it would arrive at perihelion in the January following, 
— which it did on the 25 th of that month. The 
next return will be due in 1955. The other comet 
was discovered by Olbers at Bremen, 6th March 
18 15, passed its perihelion 26th April, and was cal- 
culated to have a period of about 72 years. It was 
rediscovered by M r Brooks at Phelps, 25 th August 
1887, an d passed its perihelion 8th October; so 
that its period is not quite 721 years, and it may be 
expected again early in i960. 

All other comets of this class have much shorter 
periods, and with one exception, they attain a dis- 
tance from the Sun which 
never much exceeds that 
of Jupiter. Encke's comet 
is the most interesting. 
First discovered by Me- 
chain at Paris in 1786, 
and again independently 
by Caroline Herschel at 
Slough in 1795, an d by 
Thulis at Marseilles in 
1805, it was each time 
supposed to be a different 
body. Pons, the first to 
see it in November 1818, 
also imagined that it was 
a new comet ; but at that 
return Encke (who always 
called it Pons's comet) showed that it was moving in 
an orbit with a period of only about 3^ years, and 
that it was identical with those just mentioned. He 
predicted another return in the spring of 1822, which 
was observed in that year at Paramatta, New South 




CAROLINE HERSCHEL 
(1750-1848) 



190 



Stars and Telescopes 



Wales; and it has been seen at every subsequent 
return, passing perihelion on the last occasion in May 
1898. Its next return is due in the summer of 1901. 
Of all the periodic comets, Encke's approaches 
nearest the Sun. When in perihelion, it is very near 
the orbit of Mercury; and in 1835 ^ ma de a rather 
close approach to the planet itself, affording the 
means of determining the value of Mercury's mass. 
Even in aphelion, Encke's comet does not recede so 
far from the Sun as several of the small planets. 41 



41 This small, though very important comet, the seventh 
discovered by Miss Herschel, one of the most indefatigable 
of the early searchers for comets, was formerly just visible 
without the telescope, but at late returns it has been fainter, so 
that it cannot now be seen without optical aid. At no two- 
returns has its physical appearance been observed to be the 
same. As drawn by W. Struve in 1828, it was almost struc- 
tureless, being very like the typical telescopic comet shown on 

page 188. In 1848 it had two- 
tails, one about a degree long, 
pointing away from, and an- 
other much smaller directed 
toward, the Sun. In 187 1 
Encke's comet exhibited 
many freaks, — the nucleus at 
one time having the shape of 
a star-fish, seen obliquely at 
one side of the globular mass 
of the comet, and later a sin- 
gle straight filament or tail 
shot out a long distance from 
the coma. At subsequent re- 
turns no physical phenomena 
of especial interest have been 
developed ; it has been grow- 
ing irregularly fainter, and at 
its last return in 1894-95, it 
was first recorded, 31st October of the former year, on a pho- 
tographic plate, by D r Max Wolf of Heidelberg, and during: 




encke (1791-1865) 



Comets 191 

Another very remarkable periodic comet is that 
known as Biela's, the periodicity of which was de- 
tected at its return in 1826, when it was discovered 

the next few days it was near the limit of visibility with the 
30-inch telescope at Nice. 

At the return of this comet in 1838, Encke, the eminent Ger- 
man astronomer, then director of the Observatory at Berlin, 
was enabled to establish a remarkable progressive diminution 
in its period, amounting to about 2J hours at each return to the 
Sun, and this circumstance led to the immediate renewal of 
the old hypothesis of a resisting medium filling all space; not 
dense enough to interfere with the motions of massive bodies, 
like the planets, but of such nature as might be conceived to 
retard the motion of tenuous bodies like comets. Subsequent 
observations have fully confirmed this acceleration from a pe- 
riod of I2i2 d 79 in 1789 to i2io d 44 in 1858, as ascertained by 
Encke in the latter year; but there is no way of finding out 
whether a resistance to the comet's motion takes place every- 
where throughout its orbit, or only when near the Sun. Prob- 
ably the latter is true. The resisting medium, however, is not 
accepted by astronomers generally, because it is felt that its 
action upon other comets should be appreciable; but no such 
effect upon any other comet has ever been detected. (For the 
literature of the resisting medium, consult Houzeau's Biblio- 
graphic Generate) vol. ii. col. 680-686.) Encke continued his 
computations upon this comet down to his death in 1865; an d 
since that time his labors have been continued by von Asten 
and Backlund of Pulkowa. According to their researches, 
the progressive shortening of the comet's period, although still 
going on, was suddenly, about 1868, reduced to only half its 
former rate ; so that the theory of a resisting medium must 
either be modified, or abandoned altogether. Professor Young 
has suggested a regularly recurring encounter with a cloud of 
meteoric matter; and others have suggested a possible change 
in the physical character of the comet. Especially marked in 
the case of Encke's comet has been that apparent contraction 
of bulk (as also exhibited in several other comets) on ap- 
proaching the Sun, and the subsequent expansion when reced- 
ing from perihelion; when in this region Encke's comet is 
only -jo i ts visible diameter when it first comes into view. The 
general explanation proposed by Sir John Herschel is that 



192 Stars and Telescopes 

by Biela at Josephstadt in Bohemia, First found, 
however, in 1772 by Montaigne at Limoges, it was 
also independently discovered (being supposed, as in 
1826, to be a new comet) by Pons in 1805. The 
period was determined in 1826 to be about 6| years, 
and the comet was accordingly observed again in 1832, 
in 1845-46, and in 1852. At the second of these 
appearances it was seen to have sep- 
arated into two portions, the relative 
brightness of which fluctuated consid- 
erably, — the investigations of Hub- 
bard, of Washington, afterward show- 
ing that this disintegration probably 
occurred in the autumn of 1844. Both 
portions returned, but at a somewhat 
greater distance from each other, in 
1852. But since then the comet has 
comet n ot been seen at all, — at any rate as 
(i 9 tk February 1846) a comet, — though it is supposed that 
a shower of meteors sometimes seen 
about the end of November, when the Earth passes 
near the comet's orbit, may form part of its dispersed 
material. (See page 219.) 

Pons discovered another comet at Marseilles, 12th 
June 18 19, and Encke's investigations showed that it 
was moving in a short ellipse with a period of about 
5 \ years. It was not, however, seen again until 
1858, when it was rediscovered as a new comet by 

near the Sun a large part of the cometary substance is rendered 
invisible by evaporation, just as a cloud or fog might be. 

At the recent near approach of Encke's comet to the planet 
Mercury in 1891, D r Backlund determined anew the mass of 
that planet, making it 97^00-7000 that °f tne Sun, a value proba- 
bly too small. — D. P. 71 




Comets 193 

Winnecke at Bonn, who, after determining its orbit, 
noticed its identity with the discovery made by Pons 
nearly forty years previously. Hence it is generally 
called Winnecke's comet. It was observed again in 
1869 and 1875, but not in 1863 and 1880, when its 
positions were very unfavorable. It was observed at 
the return of 1886, and again in 1892, passing its 
perihelion in June. The period having increased in 
length, the next return came early in 1898. 

A faint comet found by M. Faye at Paris in Novem- 
ber 1843, with a period of about 7 J years, has been 
observed at every subsequent return, the last in 1895, 
when it was rediscovered by M. Javelle of Nice, 26th 
September, about six months before perihelion passage. 
It is next due in 1903. 

Brorsen's comet, discovered at Kiel in 1846 (period 
about 5J- years), and not seen in 185 1 and 1863, was 
observed in 1857, 1868, 1873, an d ^19- As it was 
not seen in 1884 and 1890, some catastrophe has 
perhaps overtaken it. M r Denning's comet of 1894 
may be a portion of it. 

In 1 85 1 d' Arrest at Leipzig discovered a small 
comet. It was found to be moving in an ellipse with 
a period of about 6 \ years, and was observed again 
(but only in the southern hemisphere at the Cape of 
Good Hope) in the winter of 1857-58. In 1864 it 
was invisible, being unfavorably placed; but it was 
observed at the returns of 1870 and 1877, though not 
in 1884. It was, however, seen again in 1890, and 
last in the summer of 1897. The next return is due 
in the autumn of 1903. 

Another comet of more than double this period, 
seen at several returns to perihelion, though not con- 
secutive, is known as Tuttle's, from its discovery by 

S <& T — 13 



194 



Stars and Telescopes 



M r H. P. Tuttle at Cambridge, Massachusetts, in 
January 1858, when its periodicity was determined. 
Previously discovered by Mechain at Paris in 1790, 
its period is about 13! years, so that it had returned 
four times without having been noticed. It was, how- 
ever, observed in 18 71, and again in 1885, when it 
passed perihelion nth September. Another return 
is due in the summer of 1899. Tuttle's comet is 
near the Earth's orbit when in perihelion, and wanders 
beyond the orbit of Saturn before reaching aphelion. 

Two comets of short period were discovered at 
Marseilles and Milan by Tempel. The first of these 
(period about six years), found in 1867, was observed 
at the returns in 1873 and 1879, passing ^ ts perihelion 
on both occasions in May ; but it has not since been 
seen, and M. Gautier has shown that the period 
has been lengthened by the perturbing action of 
Jupiter. Tempel's second, discov- 
ered in 1873 (period about 51 
years) , was observed in the autumn 
of 1878, but escaped observation 
during the subsequent returns in 
1883 and 1889. It was, however, 
re-detected near perihelion in May 
1894, and the next return is due 
in 1899. Tempel's third, found in 
November 1869, was not recog- 
nized as a periodic comet until 
after it had been rediscovered in 
swift's comet, 5th 1880 by D r Swift, then of Roches- 
april 1892 ter. So it is usually called Swift's 
(From a photograph by comet ; and the period being about 
5 1 years, an unobserved return must 
have taken place in 1875. The comet was due at 




Comets 195 

perihelion again in 1886 and 1897 ; but, as in 1875, 
it was unfavorably placed, and escaped observation on 
both these occasions. The last observed return took 
place in 1891, when the comet was detected on 28th 
September, and passed its perihelion in the middle of 
November. Another return is due in 1902. 

A bright comet discovered by D r Max Wolf at 
Heidelberg, 17th September 1884, and moving in an 
elliptic orbit (period nearly seven years), returned 
according to prediction in the summer of 1891, and 
was observed again in 1898. 

M r Fixlay at the Cape of Good Hope discovered 
a comet, 26th September 1886, which passed its peri- 
helion on 22nd November following, and has been 
calculated to have a period of about 6 \ years. A 
return duly took place in 1893 ; when the comet was 
rediscovered by M r Fixlay himself, 17th May, and 
passed its perihelion 16th June. 

A comet discovered by De Vico at Rome, 22nd 
August 1844, and calculated to have a period of 
about 5^ years, was thought to be identical with one 
observed by La Hire at Paris in 1678, between which 
time and 1844 thirty periods would have elapsed. It 
was not seen again for more than fifty years, except- 
ing that Goldschmidt obtained a single observation 
of a comet, 16th May 1855, which may have been 
De Vico's, though the identity is not proved. A small 
comet discovered by M r E. Swift on Echo Moun- 
tain, California, 20th November 1894, moves in an 
orbit very similar to that of De Yico's comet. D r 
Schulhof's researches show clearly the identity of the 
two bodies, with fluctuations in brightness : also that 
the last return was delayed by the attraction of Jupi- 
ter, which was moving near the comet in 1885-86, 
and still nearer in 1897. 



196 Stars and Telescopes 

M r Barnard discovered at Nashville, Tennessee, 
July 1 884, a faint comet with a period of nearly 5 \ years. 
It was not seen at the returns of 1889 and 1895. 

A comet discovered by M r E. Holmes at Islington 
6th November 1892, has a period of about 6| years, 
and was just visible to the naked eye for a few days. 
As it passed perihelion 20th June, nearly five months 
before discovery, a return is due in 1899. Its orbit 
is more nearly circular than that of any other comet. 

Very remarkable seems to have been the career of 
the comet of 1770, commonly called Lexell's, which 
was a truly unfortunate body in the way its motions 
were disturbed by the giant planet Jupiter. While very 
near the Earth it was discovered by Messier, 14th June 
1770 ; and a few days afterward it approached within 
a distance of little more than seven times that of the 
Moon. On calculating its orbit, Lexell found that it 
was then moving in an ellipse with a period of about 
5^ years; but that had not long been the case, for 
in 1767 it had approached Jupiter within one sixtieth 
part of the radius of his orbit, and the influence of his 
attracting mass was so powerful that the comet's course 
was completely changed. At the return of 1776, its 
position was such that it could not become visible ; 
and in 1779, before another return, it approached 
Jupiter again, much closer even than before, coming 
indeed within the distance of his fourth satellite. This 
again completely changed the comet's orbit, and made 
the period very much longer than Lexell's calcula- 
tions had determined it to be in 1770. On 6th July 
1889, M r Brooks, of Geneva, New York, discovered a 
comet moving in an ellipse of short period. D r 
Chandler showed that this body also made a very 
near approach to Jupiter in 1886, and suggested its 






Comets 



197 



identity with Lexell's comet of 1770; and the sub- 
sequent investigations of D r Poor have corroborated 
this idea. As the period of Brooks's comet is seven 
years, it was visible again in 1896. 

The above comprise all comets of short period 
known to return. 42 One discovered by Pigott in No- 



42 For convenient reference, the returns of many periodic 
comets are here tabulated, from 1898 onward: — 

Returns of Periodic Comets 



Date of 
Return to 


Periodic 
Time 


Name of Comet 


Apparitions 
Previously 


Perihelion 




Observed 




Years 






1898 April 


5.818 


PONS-WlNNECKE 


6 


1898 May 


3-303 


Encke 


27 


1898 June 


8-534 


Swift (1889 vi) 


1 


1898 June 


6.821 


Wolf (1884 hi) 


2 


1898 September 


6.507 


Temper (1867 n) 


3 


1899 January 


8.687 


Denning (1881 v) 


1 


1899 March 


33.178 


Tempel 4 (1866 1) 


1 


1899 April 


6.309 


Barnard (1892 v) 


1 


1899 May 


13.760 


Tuttle (1858 1) 


4 


1899 May 


6.909 


Holmes (1892 in) 


1 


1899 July 


5.2II 


Tempel 2 (1873 n ) 


3 


1900 February 


6.622 


Finlay (i886vn) 


2 


1900 July 


5.800 


De Vico-Swift 


4 


1900 October 


5-398 


Barnard (1884 11) 


1 


1 90 1 January 


5.456 


Brorsen (1846 III) 


5 


1 90 1 August 


7480 


Denning (1894 1) 


1 


1 901 August 


3-303 


Encke 


28 


"1902 December 


5-534 


Tempel 3 Swift 


3 


1903 September 


7.566 


Faye (1843 ni ) 


8 


1903 November 


7.073 


Brooks (1889 v) 


2 


1903 November 


6.691 


d'Arrest (1851 11) 


6 


1910 June 


76-37 


Halley 


9 


1955 March 


71.48 


Pons-Brooks 


2 


i960 April 


72.63 


Olbers-Brooks 


2 


i 9 8 5 


123.0 


Swift (1862 111) 


1 



For the most part these are inconspicuous objects, and some 
of them are never visible without the telescope. They can be 



198 Stars and Telescopes 

vember 1783 was thought to be moving in an ellipse 
with a period of about five years ; but this was un- 
certain, some thinking the period ten years, and, at 
any rate, the comet does not seem to have been ob- 
served either before or since. Also, one that was dis- 
covered by M r Denning of Bristol, 4th October 1881, 
has a period of about nine years ; but the comet has 
not been seen since, probably owing to perturbations, 
as it approaches the paths of several planets. 

Other remarkable comets, possibly seen at more 
than one return, cannot yet be classed as periodic 
bodies. Great similarity has been noticed between 
the elements (so far as they could be determined from 
descriptions of its course) of the splendid comet of 
1264 and those of the fine comet observed in 1556, 
about the time of the abdication of the Emperor 
Charles the Fifth. This was first pointed out by 
Dunthorne in 1 75 1, and attention was afterward spe- 
cially called to it by Hind, who thought it extremely 
probable that these were two consecutive appearances 
of the same comet, and that it had returned after a 
sojourn of about three hundred years in the depths of 
space. The effect of planetary perturbation would 
delay another return, which, on the whole, was thought 
most likely to take place about i860. Neither then, 
however, nor at any time since, has the comet put in 
an appearance. The cause of this is as yet unknown ; 

found by means of ephemerides, or tables of their positions 
among the stars, published in advance in the technical jour- 
nals. Generally one or more telescopic comets may be seen at 
any time, and a telescope of ten inches aperture would have 
shown no less than seven comets visible at one time in Novem- 
ber 1892. The total number of comets always present in the 
solar system has been estimated by Kleiber (on certain hypo- 
thetical conditions) to be nearly 6,ooo. — D. P. T. 



Comets 199 

but it may be remarked that while the aphelion of 
Halley's comet is at about the distance of Neptune, 
a comet with a period of three hundred years would 
pass far beyond this outer planet of our system. 

A comet observed by Tycho Brahe and others in 
1596 appears to have elements similar to those of the 
third comet of 1845 ; and the two may be identical, 
with a period of about 25c years. 




THE GREAT COMET OF 1 843 

(On 2&th February, the day after its perihelion passage 
this comet was distinctly visible to the naked eye at noo7i. 
Its approach to the Sun was the nearest ever made by any 
known comet, portio?is of its C07na being less than 50,000 
miles from the Surfs surface- Its velocity at this time 
was at the rate of about 1,280,000 miles per hour, and the 
length of its tail 150,000,000 miles) 



In the autumn of 1882 there was much discussion 
of the question whether the great comet then visible 
had any connection with the fine comets of 1843 aR d 
1880, or these with each other, or with any seen in 
bygone centuries. It is an undoubted fact that all 
the orbital elements of the comets of 1843, 1880, 



200 Stars and Telescopes 

and 1882, are very similar to each other; and it is 
probable that the comet of 1668, though very imper- 
fectly observed, had similar elements also. When at 
perihelion, all these comets made remarkably close 
approaches to the Sun, coming within a distance of 
700,000 miles of his centre, or about 300,000 miles 
of his surface. Hence it was suggested that the tre- 
mendous attractive force exerted by the Sun at so 
small a distance might greatly shorten the period at 
each return, and lead before long to the comet's absorp- 
tion into the Sun, producing an incalculable outburst 
of solar heat. On the other hand, similarity of orbit 
in two or more bodies does not prove identity of those 
bodies, it being quite possible that two or more comets 
may move along the same orbit at great distances from 
each other. Moreover, the best determinations of the 
orbit in which the comet of 1882 was actually moving 
agree in assigning about 750 years as its period, and 
it is probable that all these comets are travelling along 
the same orbit, in about that same period. 43 An addi- 

43 This singular object, the most recent great comet on rec- 
ord, was discovered early in September 1882, by many observers 
in the southern hemisphere. Also D r Common at Ealing, 
England, on the forenoon of the 17th, saw it as a bright object 
near the Sun; and so brilliant was it that M r Finlay and D r 
Elkin at the Cape of Good Hope actually followed it up to 
the very limb of the Sun itself. Here it utterly vanished, 
as if behind the solar disk ; but in fact it passed in transit 
between the Earth and our central luminary, and became visible 
on the opposite side of the Sun the following day. Although 
it had passed within 300,000 miles of the solar surface, still 
there was no appreciable acceleration due to a supposed resist- 
ing medium ; and D r Kreutz, who discussed the observations 
of its position, found that it is moving in a very elliptic orbit, 
with a period of between 800 and 1000 years. The extraordi- 
nary brilliancy, and the long period of visibility of this comet, 
permitted the successful application of photography to the de- 




gale's comet photographed at the lick observatory, 3d May 1894 

{By Professor Barnard with the 6 in. W 'Mar d lens, exposure z\ hours. The long star- 
trails indicate an tmusually rapid motion of the cornet among the stars. The 
come? s tail was about io° long, and the original plate showed its tendericy to split into 
several narrow filaments) 



Comets 20 1 

tional member of this comet family was discovered, 
1 8th January 1887, which was conspicuous for a few 
days in the southern hemisphere, though never visible 

lineation, not only of the comet's features, but also of the lines 
in its spectrum. At one time its tail was single and nearly 
straight ; at another, there were two tails slightly curved. But 
the most curious phenomena were those exhibited at its head, 
which, during recession from the Sun, underwent a remarka- 
ble subdivision into three or four, and, according to some ob- 
servers, six or eight, distinct cometary masses. Stranger still 
was the anomalous sunward extension of the coma, or sheath, 
in a vast envelope 4,000,000 miles in diameter. All told, the 
great comet of 1882 is perhaps the most remarkable on record, 
and the continued eccentricities of its physical development 
were, no doubt, the legitimate product of disturbances brought 
about by its near appoach to the Sun. 

But even more vivid in memory, doubtless, is the great comet 
of the year preceding, discovered by M r Tebbutt in Xew 
South Wales, 22d May 1881, and regarded by some observers 
as a more striking object than Coggia's comet of 1874. Mov- 
ing rapidly northward, it shone as a brilliant object in the 
northern heavens through the month of June, and was the 
first comet satisfactorily recorded by photography, — Draper 
in New York, and Jaxssen in Paris securing successful pic- 
tures almost simultaneously. D r Meyer measured with great 
care the positions of stars traversed by this object, and found 
evidence of refraction of the stellar rays by the comet, although 
in no instance was there any perceptible absorption of the star's 
light. Celestial photography has been of the greatest service 
in cometary astronomy, — the long exposures regulated to con- 
formity with the comet's motion making it possible to secure 
most of the physical features satisfactorily. When a comet's 
own motion is rapid, and its exposure long, all the stars appear 
as trails, instead of bright points, as shown in the photograph 
of Gale's comet (opposite page). Also a comet has been first 
discovered with the assistance of photography, by D r Barnard 
at the Lick Observatory, 12th October 1892. His photographs 
of Brooks's comet of 1893 show rapid and violent changes in 
the tail, as if shattered by an encounter with a swarm of 
meteors. Also a comet was discovered by M r Chase of the 
Yale Observatory, on several plates exposed for the Leonids 
in November 1898. — D. P. T. 



202 Stars and Telescopes 

in the northern. It should, however, be remembered 
that the few and uncertain observations of the comet 
of 1668 scarcely admit any decided conclusion with 
regard to its path. The tail only was visible in Eu- 
rope • and our knowledge of the comet's orbit is 
chiefly derived from a map of its course in the heavens, 
laid down from some very rough observations made 
in the East Indies, extending over an interval of less 
than a fortnight. But they indicate that this object is 
probably moving in the same orbit as the comets of 
1843, 1880, 1882, and 1887 are. 

In modern times comets which would otherwise 
have eluded detection have been ' caught,' in passing 
near the Sun while the latter was totally eclipsed. A 
photograph of the eclipse of 17th May 1882, taken by 
D r Schuster in Egypt, clearly depicted such a 
stranger in the rays of the outer corona (shown in the 
illustration on page 86). Its momentary detection 
was due to the obscuration of the Sun's light by the 
Moon when the photograph was taken. As this body 
was not visible either before or afterward, nothing is 
known of its orbit, and probably its motion was very 
rapid. This comet was called ' Tewfik/ after the 
then Khedive of Egypt. Another, much fainter and 
more difficult to recognize, was photographed in the 
corona during the total eclipse of 16th April 1893, 
by M r Schaeberle in Chile, and by other expeditions 
in South America and West Africa. 44 

44 The earliest comet detected during a total eclipse of the 
Sun was recorded by Seneca; and during a similar obscura- 
tion, probably total, slightly south of Constantinople, 19th July, 
A. D. 418, another was discovered. On a sketch of the corona 
of 1 8th July i860, by Winnecke at Pobes, Spain [Mem. Acad. 
I?uperiale, St Pete?'sbonrg i vii. Serie, t. iv. 1), is a curious struc- 
ture, which, according to Ranyard, may have been due to a 



Comets 



203 



Of comets moving in elongated ellipses approaching 
in form to parabolas, many require several thousand 
years to complete a whole 
revolution, and they are 
observable for so small a 
proportion of their whole 
course that its length can- 
not be determined with 
accuracy. The revolution 
of the great comet of 
1858 (known as Do- 
nates) is accomplished 
in about 2,000 years ; 
the splendid comet of 
181 1 has a period of 
more than 3,000 years ; 
the fine comet discovered 
by M. Coggia at Mar- 
seilles in 1874 (the 
sheaths of the coma of 
which are illustrated on 
page 205) has been com- 
puted to be moving in 




DONATl'S COMET (1858VI) 

{Drawn by G P. Bond, $th Octo- 
ber. The bright object near the 
comet" 1 s head is Arcturus, over which 
the comet passed the following- day, 
withorit appreciably dimming the 
star's light) 

an orbit of more than 



comet ; also, on the Indian photographs of the total eclipse of 
12th December 1871, a comet is thought to have been recorded 
{Monthly Notices Royal Astronomical Society, xxxiv. 365). It is 
a singular coincidence that the four modern eclipses during 
which comets were either seen or suspected are separated by 
intervals of about eleven years. Among other comets seen at one 
apparition only, 1847 vr i s interesting from the circumstances of 
its discovery, at Nantucket, 1st October, by Miss Mitchell, to 
whom a gold medal was awarded by Christian the Eighth, 
king of Denmark. Madame Rumker also discovered it inde- 
pendently at Hamburg ten days later. A recent discussion of 
its motion by Miss Margaretta Palmer of the Yale Obser- 
vatory assigns to it a hyperbolic orbit. — D. P. T. 



204 



Stars and Telescopes 



10,000 years' period; and others have orbits of even 
greater duration. All the comets of short period 
move round the Sun in the same direction as the 
planets \ 45 but many of those (including Halley's) 

45 The chemical composition of comets has been investigated 
by means of the spectroscope, — this instrument having been 
first used for this purpose in 1864 by Donati, who applied it 

to Tempel's comet of 
that year, disclosing 
the fact that these 
bodies are in large 
part self-luminous. 
Huggixs found the 
spectrum of WlN- 
necke's comet (1868 
n) to coincide with that 
of olefiant gas in a 
vacuum tube; but it 
was not until the ap- 
pearance of Coggia's 
comet (1S74) that the 
full capabilities of the 
new method could be 
tested. This brilliant 
object revealed the five 
bands of the complete 
hydrocarbon spectrum 
shading off on one 
side; but there was also a relatively faint continuous spec- 
trum, showing that while the gaseous portions of the comet 
were largely compounded of carbon and hydrogen, its light 
was in part reflected from the Sun. Researches on cometary 
spectra were continued by Vogel, Hasselberg, Young, and 
others. The comet of 1SS1. known as Tebbutt's, or (1881 III), 
was the first one whose spectrum was photographed, by Dra- 
per in Xew York, and Huggixs in London, disclosing bands 
in the violet due to carbon compounds, and showing an iden- 
tity with hydrocarbons burning in a Bunsen flame. Then came 
the two comets of 1882, approaching very near the Sun, and 
displaying the bright lines due to sodium, whose brightness 
increased as the distance of the comets from the Sun dimin- 




MARIA MITCHELL (1S1S-1SS9) 



Comets 



205 




which travel in long elliptic orbits, and many whose 
paths are parabolas, have retrograde motion. Tempel's 
comet of 1866 (the comet of shortest known period 
combined with retrograde motion) travels round the 
Sun in rather more 
than $$ years, and 
is intimately asso- 
ciated with the 
stream of Novem- 
ber meteors, or 
Leonids, as will be 
related in the next 
chapter. 

ished. Xear perihelion 
the hydrocarbon 
bands were very faint 
or wholly invisible; 
and this behavior is 
regarded by D r Schei- 

NER as proving that the intrinsic light of these comets had its 
origin in disruptive discharges of an electric nature in their 
interior. Also Dr Copelaxd, now Astronomer Royal for 
Scotland, detected in the spectrum of the September comet of 
1882 five other bright lines in the yellow and green, due to the 
vapor of iron. Xo bright comet has since appeared. It is 
interesting to note, in the observations just related, a partial 
confirmation of the theories of Dr Bredichin, previouslv 
stated, according to which the length and curvature of comets' 
tails depend upon an electrical repulsion varying with the 
molecular weight of the repelled gases. The comets of 1881 
and 1882, largely made up of hydrocarbon compounds, pre- 
sented the second type of tail, as indicated by theory. Whether 
the long, straight tails of the first tvpe are hvdrogenous in 
origin, and the shortest bushy tails of the third tvpe are due to 
the vapor of iron and other heavy substances, can be decided 
only when bright objects of these separate classes shall have 
made their appearance in the future. — D. P. T. 



the head of coggia's comet 

\lth July 1874 (Brodie) 



206 Stars and Telescopes 

Bessel, Several papers in Astron. Nachrichten, xiii. (1836). 

Herschel, J. F. W., ' Halley's Comet/ in Cape of Good Hope 
Astronomical Observations (London 1847). 

Hind, The Comets: a descriptive treatise (London 1852). 

Watson, A Popular Treatise on Co??iets (Ann Arbor i860). 

Hoek, ' Comet Systems/ Recherches astron. de V Observatoire 
a" Utrecht (The Hague 1861-64). 

Bond, G. P., ' Donati's Comet/ Annals Harvard College Ob- 
servatory, iii. (Cambridge, U. S. 1862). 

Carl, Repertorium der Co??ieten-Astronomie (Munich 1864). 

Herschel, J. F. W., Familiar Lectures on Scientific Subjects 
(New York 1866), p. 91. 

Huggins, Philosophical Transactions, clviii. (1868), 556. 

Watson, Theoretical Astronorny (Philadelphia 1868), 536, 638. 

Tait, Proceedings Royal Society Edinburgh, vi. (1869), 553* 

v. Oppolzer, Bahnbestimmung, 2 vols. (Leipzig 1870-1880). 

Zollner, Uber die Natur der Cometen (Leipzig 1872). 

V. Asten, Theorie Encke'schen Cometen (St Petersburg 1872). 

Kirkwood, Comets and Meteors (Philadelphia 1873). 

Gylden, Calcul des Perturbations des Co?netes (Stockholm 1877). 

Guillemin, The World of Comets (London 1877). 

Houzeau, Annuaire de V Observatoire Royal (Brussels 1877). 

Bredichin, Annates de r Observatoire de Moscou, iii. (1877), et 
seq. : Copernicus, \. (1881); ii. (1882) ; iii. (1884). 

Norton, ' Physical Theory/ Am. Jour. Science, cxv. (1878), 161. 

Wilson, ' Comets of 1880-83,' Publ. Cincin. Obs., Nos. 7 and 8. 

Winlock, W. C, 'Comet of 1882/ Wash. Obs, 1880, App. I. 

Peirce, Ideality in the Physical Scie?ices (Boston 1881). 

Copeland and Lohse, Copernicus, ii. (1882), 225. 

Young, Boss, Wright, and others, 'Comet 1881 b' American 
Jour?ial of Science, cxxii. (1881). 

Meyer, 'Comet of 1881/ Archives Sciences Geneve, viii. (1882). 

Huggins, Proc. Royal Institution, ix. (1882); x. (18S3), 1. 

Backlund, ' Encke's Comet/ Mem. Acad. Imperiale Sciences 
St Petersbourg, xxxii. (1884) ; xxxiv. (1886) ; xxxviii. (1892). 

Gill, ' 1882/ Ann. Roy. Obs. Cape of Good Hope, ii. (1885), pt. 1. 

Weiss, ' Bericht/ Viertel. Astron. Gesell. xx. (1885), 287. 

Newton, ' Biela's Comet/ Amer.Jour. Science, cxxxi. ( 1886), 81. 

Unterweger, Denk. Akad. der Wissenschaften Wien (1887). 

Proctor, Popular Science Monthly, xxxi. (1887), 50. 

Harkness, ' Orbit Models/ Sidereal Messenger, vi. (1887), 3 2 9« 

Thollon, Annates de V Observatoire de Nice, ii. (1887). 

Boss, ' Comet Prize Essay/ Hist. Warner Obs. (Rochester 1887). 



Comets 207 

LANGLEY, The New Astronomy (Boston 1888). 

Berberich and Deichmuller, ■ Brightness of Encke's Comet,' 

Astrouo/nisc/ie A r achrichten, cxix. (1888); cxxxi. (1893). 
Chambers, Descriptive Astronomy, vol. i. (London 1889). 
Hirn, Constitution de f Espace Celeste (Paris 1889). 
Plummer, 'Comet Groups,' Observatory, xiii. (1890), 263. 
Kirkwood, ' Age,' Publ. Ast. Soc. Pacific, ii. (1890), 214. 
Peters, C. F. W., Himmel und Erde, ii. (1890), 316. 
TlSSERAND, 'Origin/ Bulletin Astroncmigue, vii. (1890), 453. 
Callandreau, Ann. Obs. Paris, Memoires, xx. (1890). 
Denning, 'Comet-seeking,' Telescopic Work (London 1891). 
Newton, ■ Capture of Comets by Jupiter,' Am. Jour. Science, 

cxlii. ( 1 89 1 ); Memoirs National Academy of Sciences, vi. ( 1893). 
Barnard, 'Classification/ Astronomical Journal, xi. (1892), 46. 
Clerke, History of Astronomy (London 1893), I0 9> 39 2 > 4 l 7- 
Wilson, ' 1SS9 v/ Popular Astronomy, i. (1893), T 5 T - 
Scheiner and Frost, ' Spectra of Comets/ Astronomical 

Spectroscopy (Boston 1894). 
Galle, Verzeichniss der Ele??iente der bisher berechneten Cometen- 

bahnen (Leipzig 1894). 
Lynn, ' History of Encke's Comet/ Nature, li. (1894), 108. 
Olbers, Sein Leben und Seine Werke (Berlin 1894). 
Spitaler, Denk. Akad. Wissenschafteu Wien, lxi. (1894). 
Plummer, Jour. Brit. Astr. Association, iv. (1894), 89. 
Holetschek, Denk. Akad. Wisse7ischaften Wien, lxiii. (1896). 
MuLLER, Photometrie der Gestirne (Leipzig 1897). 
Lynn, Remarkable Co?nets (London 1898). 
Payne, 'Comet Families/ Popular Astronomy, vi. (1898). 

The keen popular interest in comets is responsible for a vast 
literature which is excellently represented by the long lists of 
titles in the Indexes of Poole and Fletcher. The later vol- 
umes of these invaluable indexes contain also many titles of 
scientific papers ; but the fullest acquaintance with them will 
be greatly facilitated by reference to Houzeau's Vade Mecu?n 
de V Astronome, and his Bibliographic Generate, ii. (Brussels 
1882). Comet literature since that date is best summarized in 
Bulletin Astronomique, a Paris monthly, begun in 1884; also 
the concise notes in the annual reports of the Smithsonian 
Institution are helpful. Current information concerning comets 
is given in the Annuaire du Bureau des Longitudes, the astro- 
nomical notes in Nature, and in Knowledge, The Observatory^ 
and Popular Astronomy, — D. P. T 



CHAPTER XIII 



METEORIC BODIES 



/"^OMETS have been for about two hundred years 
^- / recognized as cosmical bodies, often travelling 
in regular orbits round the Sun ; but that swarms of 
meteoric bodies move in a similar manner has been 
known during only the last sixty years. 46 

46 The true cosmic nature of luminous meteors has, however, 
been recognized a full century ; earlier they were regarded 

purely as phenomena 
of the upper atmos- 
phere, in origin as well 
as manifestation. 
While Halley and 
others seem to have 
had a vague notion of 
the insufficiency of this 
view, the German phi- 
losopher Chladni, 
celebrated for investi- 
gations of the laws of 
sound, seems to have 
first expressed the true 
conception of meteoric 
matter, having pub- 
lished in 1794 the view, 
essentially unmodified 
to-day, that interplane- 
tary space is tenanted 
by shoals of moving 
bodies, chiefly iron, ex- 
ceedingly small in mass 
and dimension as compared with the planets. Multitudes of 
these minute bodies, then, collide with the Earth while it is 




v: 



CHLADNI (1756-1827) 



Meteoric Bodies 209 

The first definite establishment of the relation of 
such a swarm to the solar system is principally due to 
the labors of Professor Newton of Yale University, in 
the case of the November meteors. The recurrence 
of the shower as seen in the United States, 13th No- 
vember 1833, on about the same day of the year that a 
like shower had been witnessed by Humboldt and 
Bonplaxd in South America 34 years earlier (12th 
November 1799), led to a careful examination of pre- 
vious accounts, and to the discovery of evidence that 
a shower radiates from the same point in the heavens 
about that time every year. 47 It happens later by 

travelling through a shoal of them ; and by their impact with 
the upper regions of our atmosphere, and by friction in passing 
swiftly through it, are heated to incandescence, thus presenting 
the luminous phenomena commonly known as shooting stars. 
For the most part they are consumed or dissipated before 
reaching the solid surface of our planet. The fact is deter- 
mined from theory and well established from observation 
that more meteors are seen during the morning hours (from 
4 to 6 A. M.J than at any other nightly period of equal length, 
because the sky is then nearly central around that general di- 
rection in which the Earth is moving in its orbit about the Sun ; 
and to the meteors which would fall upon the Earth if it were 
at rest must be added those overtaken by reason of our own 
motion. Also it is now recognized that from July to January, 
while the Earth is passing from aphelion to perihelion, more 
meteors are seen than during the first half of the year ; but 
this seems to be chiefly because the rich shoals of August and 
November are then encountered. — D. P. T. 

47 This point is situate in the constellation Leo, and the 
meteors of this shower are therefore known as Leonids. They 
have fallen at 33-year intervals since A. D. 902. Their average 
velocity on reaching the Earth is about 44 miles per second. 
Meteors when encountered by our atmosphere are moving 
through space in lines essentially parallel ; a fact of the first 
order of significance, which Twining and Olmsted in 1834 
were the earliest to recognize. Indeed, they actually suggested 
S &T — 14 



210 Stars and Telescopes 

about two days each century ; . but it is especially 
brilliant and conspicuous at the end of each interval 

the cometary character of the November shower. The appar- 
ent phenomena of a great shower are well illustrated in the 
opposite chart of a fall of August meteors, or Perseids, in which 




DENISON OLMSTED (179I-1859) 

the apparent path of each meteor in the heavens is carefully 
laid down, and the seeming radiation from a central point, 
wholly due to perspective effect, is made clear. These appar- 
ent paths are the projected sections of orbits described by the 
meteors round the Sun, and intersecting our orbit. If a meteor 
were met by the Earth head on, it would of course be charted as 
a mere point at the centre, or radiant ; those meteors nearest to 
this position have their luminous courses most foreshortened, as 



Meteoric Bodies 2 1 1 

of 33 or 34 years. Professor Newton showed that 
the bodies must move in one of five w r ell defined 

represented by the shortest arrows ; while those farthest from 
the radiant are visible through the longest apparent course 
among the stars. Accurate observation of the tracks of me- 
teors is very difficult ; and on every shower-chart will be found a 
few arrows whose prolongation does not pass near the radiant. 




THE APPARENT RADIATION OF METEORS 
(Denning) 

{A shower of Perseids, tJte arrows showing the vis- 
ible path of each meteor observed, and their pro- 
longation backward defining tlie position of the 
radiant i?i the sky} 



212 Stars ci7id Telescopes 

orbits to satisfy this delay ; but the investigation of 
Adams, of Cambridge, England, showed that one only 
of these would explain all the circumstances of the 

Stray or sporadic meteors are often thus indicated, as well as; 
the effects of imperfect observation. 

D r Max Wolf of Heidelberg, having exposed a plate an 
hour for the stars of the Milky Way, 7th September 1891, found 




APPARATUS FOR PHOTOGRAPHING TRAILS OF METEORS 

{An inclined or polar axis driven by clockwork, so as to follow the stars 
accurately . Upon this axis are mounted several cameras which can be 
so pointed as to cover a selected portion of the sky. Then, the clockwork 
being started, and the caps removed, each luminous meteor makes its o wit 
exposure, audits trail is impressed among the stars upon the plate with- 
absolute precisioii ) 

on development a fine, dark, nearly uniform line crossing it, due 
to a meteor of uneven brightness in its flight ; and this is the 
first meteor trail ever photographed (see also page 359). Du- 
ring the showers of 1894, Professor Newton and D r Elkin 
of New Haven brought into successful service at the Yale 
Observatory the novel piece of apparatus pictured in the ac- 




WINNECKE (1835-1897) 
^Friedrich August Throdor W is neckk was an astronomer of unusual 
talent and exceptional versatility, as shown by his extensive researches 
in both theoretic and observational astronomy, especially relating to the 
comets {p. 193). He was for a time Vice-director at Ptdkowa) 




N EWTON ( 1 83O- 1 896 ) 
(Hubert Anson Newton, late Professor of Mathematics at Yale, besides 
his classic researches on the connection between comets and meteors, 
Proved in 1875 the origi7i of comets extraneous to the solar system ; and 
he showed how planets, Jtipiter especially, capture these bodies) 



Meteoric Bodies 



213 



case. This true explanation is that the swarm of me- 
teors, of which the November shooting-stars form a 
portion, moves round the Sun in a regular elliptic 
orbit, with a period of about 
33i years ; and that the peri- 
helion of that path, where the 
meteors are of course nearest 
to the Sun,very nearly touches 
the Earth's orbit, as indicated 
by the accompanying dia- 
gram. 

The Earth, passing through 
that point of its orbit in the 
middle of November, encoun- 
ters meteoric matter on every 
such occasion; but the me- 
teors being much more closely 
aggregated in a certain por- 
tion, called the ' gem of the 
ring/ the most abounding 
showers occur only every 

thirty-third year. As, however, the ' gem ' extends a 
great distance along the line of the meteoric orbit 
(about, in fact, ^ ■ part of its whole length) , fine 
displays are generally seen on several years in succes- 




PATH OF THE NOVEMBER ME- 
TEORS AND OF TEMPEL's 
COMET (1866 i) 

{In relation to the planetary 
orbits, to which it is inclined 
in sfiace about 17 ) 



companying illustration ; and by means of it the trails of bright 
meteors have been located among the stars impressed on pho- 
tographic plates, with a precision wholly unattainable by the 
purely optical methods of the past. These investigations are 
conducted at the charge of a trust fund of the National Academy 
of Sciences, provided by the late D r J. Lawrence Smith, 
whose researches added very greatly to our knowledge of the 
meteorites. The principal of this fund, about $8000, was 
derived from the sale of D r Smith's splendid collection of 
meteorites to Harvard University. — D. P. T. 



214 



Stars and Telescopes 



sion. The orbital motion of these meteors, like that 
of many comets, is in a reverse direction to that of 
the planets ; and this of course greatly increases the 
relative velocity with which a portion of them enter 
the Earth's atmosphere, while the larger part of the 
mighty stream sweeps on nearly toward the part of 
space which the Earth has left. The aphelion of 
their path is a little beyond the orbit of Uranus. As 
a result of these investigations, another grand display 
of meteors was predicted for 14th November 1866; 
and this was strikingly verified. 48 

48 Like displays are expected, 14th November 1899 and 1900. 
Sometimes astronomers when sweeping the sky for comets 
encounter small meteoric bodies in 
their search. A remarkable flight 
of faint, telescopic meteors was thus 
observed by Professor Brooks, 28th 
November 1883, as depicted in the 
accompanying illustration. They 
were very small, and most of them 
left a faint train, visible in the tele- 
scope for one or two seconds. M r 
Denning estimates that the tele- 
scopic meteors are twenty-fold more 
numerous than the naked- eye ob- 
jects of this nature. At rare inter- 
vals telescopic views of very large 
meteors, usually called fireballs, or aerolites, have been caught, 
and all these physical phenomena are doubtless of the same 
general character, although variously represented by the differ- 
ent astronomers who 
have been favored 
with the opportunity 
of making such ob- 
servations. Gener- 
ally the individual 
particles are seen to 
be balloon-shaped. 
Above is an excellent picture of the disintegration of a slow 




FLIGHT OF TELESCOPIC ME- 
TEORS, 28th November 1883 
(Brooks) 




METEOR OF 28th DECEMBER 1888 (DENNING) 



Meteoric Bodies 



215 



Not long afterward the meteors seen about 10th 
August were subjected to a similar examination, with 
the result that they too 
move in an elliptic orbit 
round the Sun in a re- 
verse direction to that 
of the Earth and plan- 
ets; but their path is 
much more eccentric 
than that of the No- 
vember meteors, and 
though at perihelion it 
meets the Earth's orbit, 
at aphelion it stretches 
far beyond Neptune. 

These discoveries 
were speedily followed 
by another, priority in 
which belongs to Pro- 
fessor SCHIAPARELLI of 
Milan. It is that each 
of these meteoric orbits 
is identical with that of 
a comet, which bodies 
must therefore be re- 
garded as sustaining 
very close and intimate 
connection with the me- 
teors. The orbit of the 




PATH OF THE AUGUST METEORS 
{In relation to the Earth's orbit, which 
is represented by the small ellipse. 
Around it are the numbers of the 
months. Only the perihelion portion 
of the meteoric path is shown, and 
its intersection with our orbit is at 
the point where the Earth is about 
10th August. The radiant of this 
shower is in the constellation Perseus)- 



moving meteor in its aerial flight, as drawn by M r Denning, of 
Bristol, England, who ranks among the foremost of living au- 
thorities on meteoric astronomy. At the last phase the pear- 
shaped body spread into a wide stream of fine ashes and disap- 
peared. Such celestial displays are most likely in April, Au- 
gust, November, and December. — D. P. T. 



2l6 



Stars and Telescopes 



November meteors 49 has the same elements as that 

49 So systematically have meteoric phenomena been watched 
and recorded during the past quarter century, particularly by 
the Italian astronomers, that nearly 300 distinct showers are 
now recognized. Following is a selected list of those observed 
in recent years by M r Denning at Bristol : — 









Position of 










Radiant Point 








Name of 
Shower 




Dates of Observation 




Right 


j Declina- 








Ascension 


tion 








Quadrantids 


h m 
15 20 



52 X. 


January 2-3 




s 


Cancrids 


7 56 


16 N. 


January 2-4 




K. 


Cygnids 


19 40 


53 N. 


January 14-20 




e 


Coronids 


15 32 


31 N. 


January 18-28 




a 


Draconids 


14 4 


69 N. 


February 1-4 




a 


Serpentids 


15 44 


UN. 


February 15-20 







Leonids 


11 40 


IO N. 


March 13-15 




P 


Ursids 


10 44 


58 N. 


March 24 




i 


Draconids 


17 32 


62 N. 


March 28 




P 


Serpentids 


15 24 


17 X. 


April 17-25 






Lyrids 


18 


32 N. 


April 17-20 




V 


Aquarids 


22 28 


2 S. 


April 29-May 6 




a 


Coronids 


15 24 


27 N. 


May 7-18 




V 


Aquilids 


19 36 


O 


May 15 




V 


Pegasids 


22 12 


27 N. 


May 29-June 4 




8 


Cepheids 


22 20 


57 N. 


June 10-28 






Vulpeculids 


20 8 


24 N. 


June 13-July 7 




a 


Cygnids 


20 56 


48 N. 


July 11-19 




a- 


j3 Perseids 


3 12 


43 N. 


July 23-August 4 




8 


Aquarids 


22 36 


12 S. 


July 27-29 




A 


Andromedes 


23 20 


51 X. 


July 30-August 11 






Perseids 


3 


57 N. 


*August 9-1 1 




K 


Cygnids 


19 28 


53 »• 


August 5-16 







Draconids 


19 24 


60 N. 


August 21-25 




e 


Perseids 


4 8 


37 N. 


August 21-September 21 




7 


Pegasids 


20 


IO N. 


August 25-September 22 




P 


Piscids 


23 4 


O 


September 3-8 




V 


Aurigids 


4 52 


42 N. 


September 12-October 2 






Lyncids 


6 36 


43 N. 


September 21-25 




e 


Arietids 


2 40 


20 N. 


October 11-24 






Orionids 


6 8 


15 N. 


October 17-20 




5 


Geminids 


7 4 


23 N. 


October 




e 


Taurids 


3 4o 


9 N. 


November 2-3 






Leonids 


10 


23 N. 


November 13-14 






Leo Minorids 


10 20 


40 N. 


November 13-28 




e 


Taurids 


4 12 


22 N. 


November 20-28 






Andromedes 


1 40 


43 N. 


November 26-27 






Geminids 


7 12 


33 n. 


December 1-14 




a 


Geminids 


7 56 


29 N. 


December 7-12 




K 


Draconids 


12 56 


67 N. 


December 18-29 



* Probably, M r Denning says, the Perseids are observable 
more than a month, during which period their radiant is con- 



Meteoric Bodies 217 

of a small comet discovered by Tempel at Mar- 
seilles, 19th December 1865, which passed its peri- 
helion, nth January 1866, and was found to have a 
period of $iy\ years. The Chinese observed a comet 
in the year corresponding to a. d. 1366, which, it is 
thought, was probably moving in an orbit identical 
with Tempel's, seen just 500 years afterward (equal to 
15 of its calculated periods). Farther, the orbit of 
the meteors of 10th August coincides with that of the 
third comet of 1862 (discovered by Professor Swift, 
15 th July, and visible to the naked eye during part of 
August and September) , which has been calculated to 
revolve round the Sun in about 120 years. The dis- 
persion of meteoric particles along the cometary 
orbit must be much more complete in the case of 
the August than of the November meteors, since 
the abundance of the former is far more nearly 
uniform. 50 

tinually shifting eastward and northerly among the stars. 
Many of the showers in the above list are as yet incompletely 
■determined, and scattering observations by amateurs are well 
worth recording. It will readily be inferred that there are few 
•clear, moonless nights when meteors can not be seen with a 
little patient watching. — D. P. T. 

50 A word concerning the origin of meteors. Many theories 
have been advanced — that they came from the Sun, from the 
Moon, from the Earth as a product of volcanic action, and so 
on ; but the difficulties barring the acceptance of these and many 
other hypotheses are very great. On the other hand, the theory 
that all meteors were originally parts of cometary masses is one 
that may be accepted without much hesitation. Comets in the 
past have been known to disintegrate, — for example, that of 
Biela, already illustrated on page 192, in its double form ; and 
its story has been admirably told by Professor Newton. Ap- 
parently the process went on so rapidly that in 1885 farther 
subdivision had taken place, and it is now exceedingly unlikely 
that any part of the comet will ever be seen again, as a comet. 




218 Stars and Telescopes 

Another interesting fact bearing upon this subject 
must be mentioned here. On 27th November the 

During the shower of the Biela meteors, 27th November 1885,, 
however, a piece of this comet fell upon the Earth, at Maza- 

pil, Mexico; and on subse- 
quent occasions we may expect, 
to capture still other fragments, 
as the Bielids enter the atmo- 
sphere with a velocity of only- 
ten miles a second. The 
strange disintegration of the 
nucleus of the great comet of 
1882 was watched and depicted 
by numerous reliable observ- 
ers ; and as it is a member of 
a cometary family, the comets 
brooks comet OF 1890 of 1 843, 1880, and 1887 being 
{In process of disintegration) fellow voyagers along the same 
(Barnard) orbit through space, it is not 

unreasonable to assume that all 
four of these bodies may in past ages have been a single comet 
of unparalleled proportions. Other comets, too, have been 
recognized as fragmentary, but only a single additional instance 
need be cited, — that of Brooks's comet of 1890, the separate 
nuclei of which are shown in the above illustration. 

Many comets, then, having been known and seen to disin- 
tegrate under the repeated action of solar forces, which forces 
are exerted in greater or less degree upon all bodies of this 
class, the theory of the secular disruption of all comets is 
reached as an obvious conclusion. From several independent 
lines of inquiry, it is known that the age of the solar system is 
exceedingly great, probably many hundreds of millions of 
years ; we should therefore expect to find almost the whole 
mass of a few comets (perhaps the older ones upon which the 
disrupting forces had been operant for indefinite ages) already 
shattered into small pieces ; so that instead of the original 
comet, we should have an orbital ring of opaque meteoric 
bodies, travelling round the Sun in the original cometary path, 
each body too small to reflect an appreciable amount of solar 
light, and only visible as a meteor when in collision with our 
atmosphere. Already the identity of four such comet-orbits 



Meteoric Bodies 219 

Earth crosses the orbit of Biela's comet, which body, 
it will be remembered, has ceased to appear accord- 
ing to calculation; and about that time showers of 
meteors have been seen to radiate from a point in 
Andromeda, from which a body moving in the orbit 
of the comet would seem to approach. A very con- 
spicuous display was seen on that date in 1872, when 
the Earth crossed the comet's orbit about three 
months after the body itself should have passed that 
point; and it was even suspected that a portion of 
Biela's comet was afterward seen receding in the 
opposite direction to that of the radiant point of the 
meteors. But this remains very uncertain, as it was 
difficult to reconcile the motion of that body with the 
theoretical motion of the comet. Another fine display 
of meteors was seen 27th November 1885, when the 
principal part of the comet was even nearer the Earth 
than in 1872. Doubtless there is some connection 
between these meteors and the comet, and the radiant 
will continue to be watched with great interest. A 
considerable shower of meteors was noticed to emanate 
from this region of Andromeda, 23d November 1892,. 
somewhat earlier in the month than previous appear- 
ances ; and it seems probable that this was a sporadic 
group, also that a larger shower may be expected near 
the end of November 1905. 

and meteor streams has been established beyond a doubt, giv- 
ing rise to the well-known showers of 20th April, 10th August, 
14th and 27th November ; and there no longer seems to be any 
substantial reason for doubting a like origin for all other mete- 
oric bodies. Meteors, then, belonged originally to comets, which 
in the lapse of ages have trailed themselves out, so that discrete 
particles of the primal mass are liable to be encountered any- 
where along the original cometary paths. — D. P. T. 



CHAPTER XIV 

METEORIC BODIES (continued) 

WITHIN very recent years, meteoric bodies have been seen 
to fall upon our globe during periods of well known 
showers ; and these objects, captured by the Earth and now in 
relatively small numbers in our cabinets and laboratories, are to 
be regarded as actual fragments of celestial bodies which were 
originally comets, but which have become disintegrated by the 
action of solar forces at their returns to perihelion. The recent 
recognition of this connection between meteorites and the 
showers of April, August, and November, breaks down the 
last objection to the theory (toward which astronomers have 
long been drifting, and which may now be accepted without 
reserve) that all luminous meteors, heretofore classified and 
subdivided as aerolites, meteoroids, shooting stars, bolides, 
siderolites, fireballs, meteorites, and the like, belong to a single 
class, and have a community of origin. Their points of differ- 
ence relate only to size, and to composition, chemical and 
physical. 

Only two general terms, then, are necessary. All those ce- 
lestial bodies colliding with the Earth and producing sudden 
and characteristic luminous phenomena of the sky are (i) me- 
teors. Sometimes they are very large, perhaps tons in weight; 
or their composition may be peculiar; or their encounter with 
the atmosphere may take place near a minimum velocity : for 
those and other reasons, meteors which resist that intense dis- 
ruptive action due to the friction of the atmosphere and the 
heat due to atmospheric impact, and fall down upon the sur- 
face of the Earth, are known as (2) meteorites. Of the last there 
are many classes, representing in all about 400 different falls, 
few of which were, however, actually seen to fall. The most 



Meteoric Bodies 



221 



celebrated collections of meteorites are at Vienna, the British 
Museum, Paris (illustrated below), Harvard University (col- 
lected by Lawrence Smith), Amherst College (collected by 
Shepard), Yale University, and Berlin. 




THE PARIS COLLECTION OF METEORITES 

{In the Museum cTHistoire Naturelle, begun by Cordier and largely 
augmented by Daubree) 



Although the descent of meteoric bodies from the sky was 
generally discredited till the beginning of the present century, 
still such falls have been recorded from the earliest times. 
Usually regarded as prodigies or miracles, such stones have 
commonly been objects of worship among the oriental peoples; 
for example, the Phrygian stone, the ' Diana of the Ephesians 



222 Stars and Telescopes 

which fell down from Jupiter/ the famous stone built into the 
Kaaba at Mecca, and to-day revered by Mohammedans as a holy 
relic. The earliest known meteoric fall is historically recorded 
in the Parian Chronicle as having occurred in the island of Crete, 
B. c. 1478. We must pass over the numerous falls of meteoric 
bodies first brought together and discussed by Chladni 
(chief among which was the Pallas or Krasnoiarsk iron, an 
irregular mass weighing about f of a ton, found in 1772 by 
the celebrated traveller Pallas near Krasnoiarsk, Siberia, and 
the greater part of which is now preserved in the Imperial 
Museum at Saint Petersburg), and devote a few words to a 
* shower of stones' in the department of Orne, France, early in 
the present century. Biot, the distinguished physicist and 
academician, who was directed by the Minister of the Interior 
to investigate the subject, reported that about 1 P. M. on Tues- 
day, 26th April 1805, there had been a violent explosion in the 
neighborhood of L/Aigle, heard for a distance of 75 miles 
round, and lasting five or six minutes. A rapidly moving fire- 
ball had been seen from several adjoining towns in a sky gener- 
ally clear, and there was absolutely no doubt that on the 
same day many stones fell in the neighborhood of L/Aigle. 
They were scattered over an elliptical area 6J miles long, and 
2\ miles broad, and Biot estimated their number between two- 
and three thousand. Thenceforward the descent of meteoric 
matter upon the Earth from interplanetary space has been 
recognized as an undoubted fact. 

Many similar phenomena since investigated show (as would 
be expected from their cosmic origin) that meteorites fall upon 
our planet without reference to latitude, or season, or day and 
night, or weather. Their temperature on entering our atmo- 
sphere is probably not far from 200 centigrade below zero, and 
their velocities range from 10 to 45 miles a second. So' great 
is the atmospheric resistance to their flight that on traversing; 
the whole of this protecting envelope, their velocity is vastly 
reduced, and very suddenly. On the basis of experiments by 
Professor A. S. Herschel, it was found that the velocity (at 
ground impact) of the meteorite which fell at Middlesborough, 
Yorkshire, 14th March 1881, was only 412 feet a second; and 
at Hessle, Sweden, 1st January 1869, several stones fell on ice 
only a few inches thick, and rebounded without either breaking 
it or being themselves broken. The flight of a meteor through 
the atmosphere is only a few seconds in duration, and owing to> 
the sudden reduction of velocity, it will continue to be lumin- 



Meteoric Bodies 



223 



ous throughout the upper part of its course only ; on the aver- 
age, visibility is found to begin at an elevation of about 70 
miles, and end at about half that altitude. The work done by 
the atmosphere in suddenly reducing the meteor's velocity ap- 
pears in considerable part as heat, fusing its exterior to incan- 
descence. But conduction of heat in stony meteoric masses 
is slow; and notwithstanding the excessively high temperature 
of the exterior, during luminous flight, there is good reason for 
believing that all large meteorites, if they could be reached at 
once on striking the Earth, would be found to be cold ; because 
the smooth, black crust or varnish, which invariably encases 
them as a result of intense heat, is always thin. 




METEORIC IRON FROM ORANGE RIVER, SOUTH AFRICA 
IN THE SHEPARD COLLECTION OF AMHERST COLLEGE 

{Extreme length 19 inches ; weight 326 lbs.) 



The Orange River meteorite of the Amherst College collec- 
tion, here photographed, is an excellent typical specimen. Par- 
ticularly are the pittings or thumb-marks, generally covering 
the exterior of iron meteorites, well shown in this specimen ; they 
are due probably to the resistance and impact of the minute col- 
umns of air which impede its progress, and to the unequal con- 
duction and fusibility of the surface material. Meteorites are 
never regular in form or spherical ; and the Orange River 
meteorite exhibits about average irregularities of exterior. 
These indicate a fragmentary character and lack of uniform 



224 Stars and Telescopes 

structure in the original mass. Often there is an explosion, 
which is in part accounted for by the sudden heat to which the 
exterior is exposed, and the impact of the air column in front 
of the swiftly moving meteor, which is so densely compressed 
that it acts almost like a solid. Fragments are sometimes 
found miles apart which fit perfectly together. 

The surface of our Earth containing three times as much 
water as land, a large proportion of all falling meteorites are 
necessarily lost in the ocean. The processes of deep sea dredg- 
ing have, indeed, in some instances brought to light an appre- 
ciable amount of meteoric matter. Of meteorites which fall 
without being seen, in regions where ordinary climatic condi* 
tions prevail, by far the greater part soon disappear because of 
atmospheric action, the irons gradually oxidizing, and the stones 
rapidly disintegrating because of their porous structure. In 
desert climates, however, their lifetime is greatly extended ; and 
in such regions the search for meteorites is best rewarded. 

Although meteorites are classified as metallic and stony, the 
division is far from abrupt. According to their structure and 
composition, the metallic meteorites are subdivided into sider- 
ites, siderolites containing 80 to 95 per cent of iron, and pallas- 
ites, the first being homogeneous masses of iron and nickel com- 
bined, while the last are spongy masses of iron filled with oli- 
vine, or chrysolite. About eleven twelfths of the stony meteorites 
(which are greatly in excess of the metallic ones) are termed 
chondrites, by Rose, because their composite structure is that 
of rounded grains (chondri), with nodules of iron generally 
scattered through their mass. Professor Newton has carefully 
investigated the history of about 265 observed falls, repre- 
sented by specimens in existing collections, and he has found 
that their motions about the Sun were direct, not retrograde. 
He concludes also that the larger meteorites moving in the solar 
system are allied much more closely to the group of short period 
comets than to the comets whose orbits are nearly parabolic. 

The largest fall actually heard or seen occurred in Emmett 
County, Iowa, 10th May 1879, m a shower of stones, the most 
massive weighing 437 pounds. The largest meteoric stone 
ever discovered weighs 647 pounds ; it fell in Hungary, in 
1866, and is now in the Vienna Museum. The iron meteorites 
are often much larger, a famous one found in Tuczon, Arizona, 
and now in the National Museum at Washington, being in the 
shape of a ring weighing about 1000 pounds, and one found in 
Texas, now in the Yale collection, weighing 1635 pounds. 



Meteoric Bodies 



225 



There are numerous others in different parts of the world, both 
in collections and still in the field, whose meteoric character is 
perfectly established, the largest of which, more than six tons 
in weight, is at Bahia, Brazil. The iron meteorites actually 
seen to fall are, however, remarkably few, as the following 
table shows. The largest is known as the Nedjed iron, and its 
weight is 130 pounds. 

Iron Meteorites seen to Fall 



Name of place 


Name of coun- 


Date of Fall 


Where 


Weight 


(or meteorite) 


try (or state) 


preserved 


Grams 


Agram 


Croatia, Hun- 


26th May 175 1 


British Museum 


282.3 


Charlotte 


gary 
Tennessee, U.S. 


1st August 1835 


British Museum 


77-5 


Braunau 


Bohemia 


14th July 1847 


British Museum 


553-2 


Tabarz 


Saxony 


18th Oct. 1854 


British Museum 


9.0 


Victoria West 


South Africa 


1862 


British Museum 


158.5 


Nedjed 


Central Arabia 


Spring, 1865 


British Museum 


59,420.0 


Nedagalla 


Madras, India 


23d Jan. 1870 


British Museum 


4)379-7 


Marysville 


California, U.S. 


1873 






Rowton 


Shropshire, Eng. 


20th Apr. 1876 


British Museum 


3,109.0 


Mazapil 


Mexico 


27th Nov. 1885 






Cabin Creek 


Arkansas, U. S. 


27th Mar. 1886 








' 7^S| 




??J% 



WIDMANNSTATTIAN FIGURES 

{Meteoric iron of Texas — Impression taken from the iron) 

S & T— 15 



226 



Stars and Telescopes 



One of the first tests applied to a mass of iron suspected to 
t>e meteoritic is that known as the 'Widmannstattian figures,' 
from von Widmannstatten of Vienna, who in 1808 pol- 
ished a piece of the Agram meteorite and etched it with acid. 
These figures have a general resemblance in all meteoric irons, 
well illustrated on p. 225, and they are sections of planes of 
•cleavage, along which chemical change of some sort has taken 
place. Their form and relative position are determined by the 
laws of crystallography. The test of the Widmannstattian fig- 
ures is not, however, regarded by modern investigators as in- 
fallible, because certain terrestrial substances exhibit them in 
-some degree, particularly the famous Ovifak masses discovered 
by Nordenskiold on Disko Island. The largest of these dis~ 




PSEUDO-METEORIC IRON DISCOVERED AT OVIFAK, GREENLAND, IN 187O 

(Length, b\feet ; weight, 20 tons. Now in the Hallo/ the Royal Acad- 
emy, Stockholm) 



puted meteorites is shown in the annexed engraving. For a 
long time these irons were thought to have had an extraterres- 
trial origin, but the opposite opinion is now generally held, 
•due chiefly to the examinations of Lawrence Smith and 
Rammelsberg. 

Chemical analysis of meteorites reveals the presence of all 



Meteoric Bodies 227- 

those elements most commonly recognized in the Earth's crust, 
— iron, nickel, sulphur, carbon, oxygen, calcium, with less of 
hydrogen, nitrogen, chlorine, sodium, cobalt, manganese, cop- 
per, and a trace of bromine, lead, and strontium. Iron is gen- 
erally alloyed with nickel, and phosphorus nearly always 
combined with both nickel and iron. Cobalt is very generally 
associated with the nickel. Hydrogen and nitrogen are present 
as occluded gases, and carbon usually appears as graphite, in 
a few cases as diamond. 

All investigations hitherto made of the question whether me« 
teorites bear any testimony as to the existence of living organ- 
isms in other worlds fail to show such existence. Chemical 
compounds new to mineralogy have been brought to light, but 
no new elemental substance has been discovered in analyzing 
meteorites, and the study of these bodies has become a depart- 
ment of mineralogy rather than astronomy. 

The Zodiacal Light. — After twilight in the western sky 
on clear moonless nights from January to April, may be seen 
the zodiacal light, a faintly luminous and ill-defined triangular 
area, expanding downward obliquely from the Pleiades to the 
northwest horizon. The illumination of this region is not uni- 
form, the central portions being the brightest and outshining 
the white luminosity of the Milky Way with a slightly yellowish 
tint. First recognized by Childrey about the middle of the 
17th century, Cassini observed it carefully from 1683 to 
1688, establishing its form and position so critically that no 
observations at the present day would appear to indicate any 
change. In the latter half of the present century this strange 
object has been carefully observed by Schmidt, Heis, Max- 
well Hall, Jones, Serpieri, and others; but there is still 
much divergence of view as to what may be the cause of the 
phenomenon. D r Wright, of Yale University, regards it as 
due to the reflection of solar rays from innumerable small 
interplanetary bodies, crowded more densely about the mean 
plane of the solar system, and in parts extending outward from 
the Sun far beyond the orbit of the Earth. It may be con- 
ceived as a vast cloud of meteoric dust, approximately lens- 
shaped in figure, still in slow process of formation from the 
debris of comets. That the zodiacal light is reflected sunlight 
has been abundantly proved by the spectroscope in the hands 
of Liais, Copeland, and Smyth, who find a short continuous 
spectrum similar to that of the Sun, possibly crossed by dark 
Fraunhofer lines, but without a trace of bright ones ; and by the 



228 Stars and Telescopes 

polariscope deftly manipulated by D r Wright, who in 1873-74 
found the light strongly polarized. This fact proves that it is 
reflected ; and the especial manner in which it is polarized in- 
dicates the Sun as its only source. 

The Gegenschein. — In this connection should be mentioned 
the zodiacal counterglow, or 'gegenschein/ first described in 
1854 by Brorsen, who gave it this name. A very faint and 
evenly diffused nebulous light, it is seen almost exactly oppo- 
site the Sun, and undergoes various changes of diameter (from 
about 3 to 15 ), and of shape (from circular to elliptical). 
Even the proximity of bright stars or planets renders it quite 
invisible ; and it can never be seen in June and December, 
because it is then crossing the Milky Way. It is best seen in 
September and October, in the constellations Sagittarius and 
Pisces. M r Barnard, whose eye has the advantage of long 
training upon comets and nebulae, has been very successful in 
seeing this faint and difficult luminosity of the midnight sky, and 
his observations with others show that it does not lie in the 
ecliptic, though always close to it, being generally displaced 
somewhat north. Apparently connected with the gegenschein 
is often seen, especially in the autumn, a zodiacal band, six or 
eight times the breadth of the Moon, lying along the ecliptic 
and crossing the entire heavens. Whether the gegenschein is 
due to abnormal refraction by our atmosphere, or to a zone of 
small planets, or to cosmic conditions connected with meteoric 
matter, is not yet satisfactorily made out. 



Chladni, Ur sprung der von Pallas entdeckten Eisenmasse 

(Leipzig 1794). 
BlOT, Memoir es de V Institut National de France, vi. (1806), pt. i. 
Chladni, Ueber Feuermeteore (Vienna 1819). 
Olmsted, 'Fall of 1833/ American Journal Science, xxv. (1834), 

363; xxvi. (1834), 132; xxix. (1836), 376. 
Benzenberg, Die Sternsch7tuppen (Hamburg 1839). 
Coulvier-Gravier, Les etoiles filantes (Paris 1847-54-59). 
Heis, Die Periodischen Stemschnuppen (Cologne 1849). 
Schmidt, Resultate aus zehnjahrigen B eobachtnngen ueber Stern' 

schnuppen (Berlin 1852). 
Smith, Numerous papers in American Journal Science (1855— 

83), and Comptes Rendus (1873-81). 
Jones, 'Zodiacal Light/ Report U. So Japan Expedition, iii. 

(Washington 1856). 



Meteoric Bodies 229 

Greg, Herschel, Glaisher, and others, Reports British As- 
sociation Advancement Science (i860 and onward). 

Buchner, Die Meteoriten in Sammlungen (Leipzig 1863). 

Rose, Beschreibung und Eintheilang der Meteor iteii (Berlin 
1864). 

Newton, ■ Shooting Stars,' American Journal Science, Ixxxviii. 
(1S64), 135; Memoirs Nat. Acad. Scie?ices, i. (1866), 291. 

iSCHiAPARELLi, ' Origine probabile delle stelle meteoriche/ 
Bull. Met. delV Osservatorio del Collegio Romano, v. (1866), 
8, 10, 11, 12. 

Phipson, Meteors, Aerolites, and Falling Stars (London 1867). 

Xirkwood, Meteoric Astronomy (Philadelphia 1867). 

Adams, ' Orbit November Meteors,' Mon. Not. Royal Astron. 
Society, xxvii. (1867), 247. 

Graham, Proceedings Royal Society, xv. (1867), 502. 

Daub REE, ' Meteorites,' Smithsonian Report for 1868. 

Rammelsberg, Die Chemische Natur der Meteoriten (Berlin 
1870-79). 

Maskelyne, ' Meteorites,' Nature, xii. (1875), 4^5» 5°4>.5 20 - 

Tschermak, ' Die Bildung der Meteoriten', Sitz. kk. Akad. 
Wissenschafte?i Wien, lxxi. (1875), 661 

Heis, Publ. Royal Observatory Miinster, i. and ii. (1875-77). 

Serpieri, 'La Luce Zodiacale,' Mem. Soc. Spettr. Ital., v. 
(1876), Appendix. 

V. Konkoly, Spectres de 140 etoiles filantes (Budapest 1877). 

Newton, ' Relation of Meteorites to Comets,' A r ature, xix. 

(1879). 3 l S>34°* 
Ball, ' Source of Meteorites,' A r ature, xix. (1879), 493- 
Lewis, ' Zodiacal light and Gegenschein,' American Journal 

Science, cxx. (1880), 437. 
Herschel, 'Meteor spectroscopy,' A r ature, xxiv. (1881), 507. 
Newton, 'Meteors,' Encyclopedia Britannica, 9th ed. xvi.(i883). 
Lehmann-Filhes, Die B estimmung von Meteorbahnen (Berlin 

1883). 

Tschermak, Die mikroskopische beschaffenheit der 7neteoriten 
(Stuttgart 1883-85). 

Meunier, ' Meteorites,' Encycl. Chimique, tome ii. (Paris 1884). 

Joule, ' Shooting Stars,' Scientific Papers, i. (London 1884), 286. 

Searle, A., ' Zodiacal light,' Proc. Am. Academy Arts and Sci- 
ences, xix. (1884), 146. 

Brezina, Die Meteoritensammlung des kk. mineralog. Hofkabi- 
netes in Wien (1885). 

Fletcher, Study of Meteorites (British Museum 1886). 



230 Stars and Telescopes 

Daubree. * Origin and structure of Meteorites/ Popular Science 

Monthly, xxix. (1886), 374. 
Newton, 4 Meteorites, Meteors, and Shooting Stars/ Proc. Am. 

Assoc. Adv. Science, xxxv. (1886), 1. 
Wendell, " Meteor Orbits/ Astron. Nachr., cxiv. (1886), 285. 
Schiaparelli, Le Stelle Cadenti (Milan 1886). 
Newton, * Biela Meteors/ American Journal of Science, cxxxi. 

(1886), 409; * Meteorite orbits/ cxxxvi. (1888), 1; also, 

cxlvii. (1894), 152. 
Denning, ■ Distribution of meteor streams/ Month. Not. Royal 

Astron. Society, xlvii. (1887), 35. 
Flight, A Chapter in the History of Meteorites (London 1887 
Huntington, * Catalogue of all recorded meteorites/ Proc* 

Am. Acad. Arts and Sciences, xxiii. (1888), 2>7- 
Denning, * August Meteors/ Nature, xxxviii. (1888), 393. 
Denning, In Chambers's Astronomy, i. (London 1889), bk\ v. 
Wright, " Zodiacal Light,' The Forum, x. (1890), 226. 
Lockyer, The Meteoritic Hypothesis (London 1890). 
Denning, * Catalogue of 918 radiants/ Month. Not. Royal 

Astron. Society, 1. (1890), 410. 
Plassmann, Verzeic/uiiss von Meteorbahnen (Cologne 1891). 
Denning, Telescopic Work for Starlight Evenings (London 

1891). 

Barnard, * Gegenschein/ The Astronomical Journal, xi. (1891 ), 
19; Popular Astronomy, i. (1894), 337' 

Ball, In Starry Realms (London 1892). 

Bredichin, Melanges Math, et Astron. vii. (St Petersburg 1892). 

Kirkwood, * Leonids and Perseids/ Astronomy and Astro- 
Physics, xii. (1893), 385, 789; ' Andromedes,' xiii. (1894), 188. 

Backhouse, Denning, and others, Me?noirs British Astron. 
Association, i. (1893), x 7 5 *"• ( 1 %9A)> I - 

Denning, * How to Observe Shooting Stars/ Popular Astron- 
omy, i. (1893-94). 

Schulhof, Bulletin Astronomique, xi. (1894), I2 ^» 22 5» 3 2 4> 4°6> 

Monck, * Radiants/ Joitr. Brit. Astron. Assoc, v. (1895), 253. 

Ramsay, 'Argon and Helium/ Nature, lii. (1895), 224, 

Farrington, Cat. of Collection, Field Museum (Chicago 1895). 

Harvey, Trans. Roy. Soc. Canada, 1896, § iii. 91. 

WiJLFiNG, Meteo7'iten in Samml. u. Liter atur (Tubingen 1897). 

Miers, 'Ancient and Modern Falls/ Sci. Progress, vii. (1898), 349. 

Wilson, 'November Shower/ Pop. Astron. vi. (1898), 502. 

Pickering, W. H., 'Leonids 1897/ An.Harv.Col.Ob.x\\.( 1898), v. 
Consult also Poole's Indexes, under Meteors and Meteorites. 



CHAPTER XV 

THE CONSTELLATIONS 

n^HE distribution of the stars visible in the north- 
^ ern hemisphere into groups, or (as they are 
usually called) constellations, was made in very ancient 
times, probably by the Babylonian star-gazers. Sev- 
eral less important or conspicuous groups have been 
added since ; and the principal constellations near the 
south pole, visible only in the southern hemisphere, 
were formed and named by the navigators of the 16th 
century, especially Pierre Dircksz Keyser (sometimes 
called Petrus Theodori) , chief pilot of a Dutch fleet 
which sailed to the East Indies in 1595. Others were 
added by Lacaille when observing at the Cape of 
Good Hope in the middle of the 18th century. 

About one hundred of the brighter stars have special 
names (Sirius, Arcturus, etc.) given them by Greek 
and Arabian astronomers or star-gazers ; but with these 
exceptions, the only way of referring to any particular 
star, until comparatively modern times, was by means 
of its place in the imaginary figure or animal which 
the constellation containing it was supposed to resem- 
ble, — for example, the star in the head of Andromeda, 
in the tip of the tail of Ursa Major, etc. 

The suggestion to designate each star by a letter of 
the alphabet placed before the name of the constel- 
lation was first made by Alexander Piccolomini, an 
Italian ecclesiastic and amateur astronomer, who pub- 



232 Stars and Telescopes 

lished at Venice in 1559 a small work on the fixed 
stars, in which he gave some rough diagrams of the 
principal constellations, with Roman letters affixed to 
the most conspicuous stars in each. The suggestion, 
however, was not generally adopted until John Bayer 
of Augsburg published in 1603 his well-known series 
of maps of the constellations, in which he designated 
each star therein marked by one of the letters of the 
Greek alphabet; and these have been universally 
adopted, Roman letters being used when the Greek 
alphabet is exhausted. Following the letter is the 
name of the constellation in the genitive case ; for 
example, a Ursse Majoris, (3 Cygni, etc. Numbers 
also (following the lists in Flamsteed's catalogue) are 
employed in the same manner, taken in the order of 
right ascension of the stars in each constellation, — 
being used exclusively for the fainter stars which have 
no letters, and in addition to them for the brighter 
stars which have. 51 

51 The tracing of constellations, fascinating as it is to the 
popular mind, is of slender importance to the modern astrono- 
mer, because he is accustomed to designate most of the stars 
which he observes, not so much by their names as by their 
numbers in standard catalogues of their positions relatively to- 
the imaginary circles described in the next paragraphs. The 
ability to recognize at sight about 100 of the principal stars of 
the firmament, is, however, well worth the little exertion it 
costs; and the helps to acquire this knowledge are abundant in 
number and simple in use. Better for the beginner than the 
star charts and atlases are the planispheres (p. 240), for reasons 
which will become apparent on using them ; and Proctor's 
Easy Star Lessons has an advantage over both, in reiterating 
the asterisms in their varying seasonal relations to vertical 
circles and the horizon. To the observer of luminous meteors 
and of variable stars an intimate acquaintance with constellation 
figures and stellar names is more important than in other lines- 
of astronomical inquiry. — D. P. T. 



The Constellations 233 

It should be noticed that in lettering the principal 
stars Bayer did not (as some have supposed) make 
the sequence of the letters follow throughout the 
order of apparent brightness. The stars in each con- 
stellation follow the old division into orders or classes 
of magnitude, and the letters given to the stars in 
each class were arranged rather according to the 
form of the figure represented than the alphabetic 
succession of the letters. This is clearly seen in 
the seven principal stars of Ursa Major, all rated of 
the second magnitude. Of these, a and /3 form the 
1 pointers,* or two stars pointing toward the Pole Star ; 
y, 8, are the two other stars of the so-called 'wain/ 
and e, f, 77, are the three in the tail of the bear, or the 
three horses of the imaginary chariot ; but every one 
must have noticed that, of these seven stars, 8 is much 
the faintest, although taken like the others as of the 
second magnitude. It should also be mentioned that, 
from occasional touching or overlapping of the figures, 
a given star has sometimes, in Bayer's original nomen- 
clature, a name by a different letter in two constella- 
tions : thus, /3 Tauri is the same star as y Aurigse ; 
a Andromedae is identical with 5 Pegasi, etc. To 
avoid confusion, astronomers have in each case dropped 
the secondary and retained only the primary desig- 
nation. Lacaille, in affixing letters to the southern 
stars, made their order correspond in most cases more 
nearly to the successive gradations of brightness than 
Bayer had done with the great mass of the constella- 
tions lettered by him. 

Full description of all the constellations would 
require many maps ; but a few remarks may be made 
upon some of the more noticeable stars and groups, 
especially those in and around the zodiac. 



234 Stars and Telescopes 

The plane of the Earth's equator, extended to the 
heavens, traces out a circle called the celestial equator 
or equinoctial, everywhere distant 90 , or a quarter 
circumference from both celestial poles. The north 
pole of the heavens is indicated in the sky by a star 
of the second magnitude very near it, called from 
this circumstance s [Stella] Polaris,' or the Pole Star. 
Similar prolongation of the plane of the Earth's orbit 
to the heavens traces out a circle called the ecliptic 
which is inclined to the equinoctial 23 28', or the 
angle between the Earth's equator and its orbit. 
These two great circles intersect at two opposite 
points called the equinoxes, or equinoctial points. 

A zone or band extending 8° on each side of the 
ecliptic is called the zodiac ; within this the Moon 
and all the large planets are always found, as the 
inclinations of all their orbits to that of the earth are 
less than 8°. The stars distributed along and around 
this zone have been formed into 12 constellations, 
proceeding eastward in the following order, — Aries, 
Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, 
Sagittarius, Capricornus, Aquarius, Pisces ; and the line 
of the ecliptic itself is divided into twelve signs (as 
they are called), each having taken its name from the 
constellation nearest to it. At the time of the earliest 
astronomical writings, the equinoctial points were in 
the constellations Aries and Libra, and they are still 
said to be at the first or initial points of these signs ; 
although in consequence of precession of the equi- 
noxes (page 22) they are now in the constellations 
Pisces and Virgo, and two thousand years hence will 
be in Aquarius and Leo respectively. 

As the vernal equinox (where the Sun crosses the 
•equator when moving northward) is situate in Pisces, 



The Constellatio7is 



235 



it is evident that six constellations of the zodiac 
(Pisces, Aries, Taurus, Gemini, Cancer, and Leo) 
occupy a more northern position in the heavens 
than the other six (Virgo, Libra, Scorpio, Sagittarius, 
Capricornus, and Aquarius), so that the former are 
visible more of the time from the northern hemi- 
sphere of the Earth than the latter are. 

The following considerations will show when these 
constellations are above the horizon at night. Al- 
though the Sun's light, diffused in our atmosphere, 
generally renders the stars around him invisible during 
the day, the place of the Sun in the heavens is always 
in the ecliptic, and therefore in the middle of the 
zodiac. On 20th March he reaches the vernal equi- 
nox, so called because it is the one passed by the 
Sun in the spring ; but, as previously mentioned, while 
that point is still called the first point of the sign 
Aries, as in ancient times, its present position is at 
the beginning of the constellation Pisces, The Sun 
is not therefore at the beginning of the group called 
Aries till near the end of April, and he passes the 
middle of it in May. Hence it follows that Libra, 
at the opposite side of the zodiac, will at that season 
be on the meridian, or due south at midnight, and 
the rest in order ; so that the annexed table gives the 
-zodiacal constellation on or near the meridian at the 
beginning of successive months : — 



January .... Gemini. 

February .... Cancer. 

March Leo. 

April Virgo. 

May Libra. 

June Scorpio. 



Julv . . . 


. Sagittarius. 


August 


. Capricornus 


September 


. Aquarius. 


October 


. Pisces. 


November 


. Aries. 


December . 


. Taurus. 



236 



Stars and Telescopes 



Before midnight each of these constellations will be 
to the east, and after it to the west, of the meridian 
during the month against which it is here placed. 
The winter Sun being south, and culminating low 
down, the portions of the zodiac on the meridian at 
night in winter are much higher in the heavens than 
those which are similarly visible in summer ; just as it 
is matter of common observation that the full Moon 
in winter runs high and in summer low. 

The most beautiful of the zodiacal constellations is 
Taurus, which has several very bright stars (one of 
the first magnitude called Aldebaran, or a Tauri) and 
contains the splendid cluster known as the Pleiades, 
also the more diffused cluster called 
the Hyades, in which Aldebaran is 
situate. Gemini is remarkable for 
two very bright stars near together, 
named Castor and Pollux, — the 
former being also designated a, and 
the latter /3, Geminorum. Leo is a 
fine group, and has perhaps (what 
few have) a little resemblance to 
the figure indicated by the name. 
The forepart of Leo has something 
the shape of a sickle, and contains- 
a star of the first magnitude, a Leonis, 
or Regulus. Virgo has only one 
bright star, to which the name Spica 
Virginis was attached by the ancients ; and it is now 
known either as Spica or a Virginis. The only other 
very remarkable star in the zodiac is the beautiful red 
object known as Antares (Cor Scorpii), the brightest 
star in the constellation Scorpio. 

With regard to the other constellations, the most 




THE PLEIADES 

{Ordinary naked- eye 
view. The tele- 
scope and photo- 
graphic plate have 
revealed nearly 
2,000 stars in this 
region, hundreds 
of which are 
shown in the en- 
larged view on the 
opposite page) 




THE PLEIADES — CLUSTER AND NEBULA 
(From photographs by the Brothers Henry of the Paris Observatory) 



238 Stars and Telescopes 

splendid is Orion, partly in the northern and partly in 
the southern celestial hemisphere. The three bright 
stars in a straight line above the middle of it (com- 




THE GREAT NEBULA IN ORION 

{Photographed by Roberts, 4th February 1889. Exposure, 3 hours 25 minutes. 
This nebula is faintly visible to the naked eye surrounding tlie -middle star 
in the Sword of Orion. See Page 260. A mong the most successful observers 
of this magnificent object, before the days of its photographic portraiture, were 
the Bonds [William Cranch, and George Phillips, father and son], suc- 
cessively Directors of the Harvard Observatory. The latter's drawing of 
the Great Nebula is unsurpassed) 



The Constellations 239 

monly called Orion's belt, but by astronomers d, c, £ 
Ononis) point in an easterly direction somewhat above 
Sirms, the principal star of Can is Major, which is the 
brightest star of the entire heavens. Of the stellar 
objects near the north pole, the seven which form 
part of Ursa Major are best known. As already men- 
tioned, a line prolonged through /3 and a points nearly 
toward the pole star. Another (carried to a con- 
siderably greater distance), through £, 77, passes very 
near to Arcturus, the principal star in Bootes : and 
one extended in the reverse direction through 5, a, 
will similarly indicate the position of Capella, the prin- 
cipal star in Auriga, and the brightest of the northern 
hemisphere. It is thought that this object has some- 
what increased in brightness of late years, and that 
Vega was formerly the brightest. 

On the opposite side of the pole star from Ursa 
Major, and at about an equal distance from it, is the 
fine group called Cassiopeia, which contains several 
bright stars arranged somewhat in the shape of an 
irregular W. IS^xt in brightness to Capella is Vega, 
the principal star of the small constellation Lyra, which, 
at the average latitude of places in the United States, 
passes very near the zenith at its upper culmination. 
To the west of Lyra is the large and scattered group 
known as Hercules ; to the east of it, Aquila, the three 
most conspicuous stars in which are near together and 
almost in a straight line, the brightest of the three, 
a Aquilae, being in the middle. Southward from Cas- 
siopeia is Andromeda, whose three principal stars 
(with the three brightest in Pegasus at one end and 
the largest star in Perseus at the other) form a con- 
figuration resembling the seven principal stars of Ursa 
Major. That star in Andromeda (a) nearest to Pegasus 



240 



Stars and Telescopes 



was regarded by the ancients, and marked by Bayer, 
as belonging to both constellations ; and the square 

formed by it and a, 
/3,y Pegasi, is called 
the ' square of Pe- 
gasus.' Nearly be- 
tween Aquila and 
Pegasus is Cygnus, 
resembling a Latin 
cross ; while be- 
tween Aquila and 
the southern part 
of Hercules is the 
northern part of 
Ophiuchus, a con- 
stellation extend- 
ing into both hem- 
ispheres, some- 
times called Serpentarius (serpent-holder), the same 
in signification as Ophiuchus, the latter word being 
derived from the Greek. m 




W. C. BOND (17S9-1859) 



Ideler, Ursprung und die Bedeutiing der Sternnamen (Berlin 

1809). 
Higgins, iVames of the Stars and Constellations (London 1882). 
Gore, An Astroiiomical Glossary (London 1893). 
West, ' Pronunciation of Arabic Star-names,' Popular Astron- 

omy, ii. (1S95), 20 9- 



Whitall, Movable Planisphere (Philadelphia). 

Phillips, Planisphere for the Latitude of England (London). 

Goldthwaite, Planisphere for Latitude 40 N. (New York). 

HARRi*SGTON,PlanisphereforLatzt7sdeofthe U.S. (Ann Arbor). 

Poole, Colas, Celestial Planisphere (Chicago). 

Dunkin, The Midnight Sky (London 1869). 



The Constellations 241 

Proctor, Half-hours with the Stars (London 1878). 
Proctor, Easy Star Lessons (New York 1882). 
Colbert, The Fixed Stars (Chicago 1886). 
Clark and Sadler, The Star-guide (London 1886). 
Jeans, Handbook for finding the Stars (London 1888). 
Young, ■ Uranography,' in his Elements of Astrono?ny (New 

York 1S90). 
Hill, R., The Stars and Constellations (New York 1891). 
Upton, ' Constellation study/ Popular A stronoiny, i. (1893-94). 
Serviss, The Popular Science Monthly, xlv.-xlvii. (1894-95). 
Also the constellations are accurately and artistically figured 

in The Century Dictionary (New York 1889-91). 
Clarke, How to Find the Stars (Boston 1893) '■> f° r use m con " 

nection with his convenient astronomical lantern. Also M r 

Bailey's 'Astral Lantern' will be found very helpful in 

learning the stars and constellations. 

Argelander, Uranometria Nova (Berlin 1843). 

Mitchel, O. M., Atlas (Cincinnati 1849), accompanying his 
edition of Burritt. 

Burritt, Geography of the Heavens, with Atlas (N. Y. 1856). 

C H AC o R N AC, A tlas Ecliptique ( Pari s 1 862 ) . 

Argelander, Atlas des Nord. Gestirnten Himmels (Bonn 1863). 

Heis, Atlas Coelestis A r ovus (Cologne 1872). 

Proctor, New Star Atlas (London 1874). 

Newcomb, Star maps in his Popular Astronomy (N. Y. 1878). 

Houzeau, Uranometrie Generate (Brussels 1878). 

Gould, Uranometria Argentina (Buenos Ayres 1879). 

Peters, C. H. F., Celestial Charts made at the Litchfield Obser- 
vatory (Clinton, N. Y. 1882). 

Johnston, Grant, School Atlas of Astronomy (New York 1884). 

"Espin, Elementary Star Atlas (London 1885). 

Schonfeld, Bonner -Sternkarten (Bonn 1886). 

Schurig, Hi?7i?nels- Atlas (Leipzig 1886). 

Messer, Stern- Atlas fiir Himmelsbeobachtung (St Petersburg 



Klein, McClure, Star Atlas (London i£ 
Cottam, Charts of the Constellations (London iS 
.Peck, Handbook and Atlas of Astroiiomy (New York 1891). 
AYeiss, Bilder-Atlas der Stern enwei 't (Esslingen 1891). 
Ball, An Atlas of Astronomy (New York 1892). 
Rohrbach, Sternkarten in gnomon. Projection (Berlin 1894). 
Upton, Star Atlas (Boston 1895). 

Peck, The Observer's Atlas of the Heavens (London 1898). 
s * T — 16 



CHAPTER XVI 

THE COSMOGONY 

npO inquire into the origin and development of the 
•** heavenly bodies is the object of the Cosmog- 
ony, or the science of the formation of the world. 

Have the planets, the Sun, and the stars always 
existed, as they now appear in the sky ; or was there 
a time when the present beauty and order of the 
Cosmos was supplanted by a state of chaos? To 
this question the cosmogony of the present time 
answers that the heavenly bodies have been gradually 
developed from a diffused or nebular condition, just 
as animals and plants are developed on the earth ; 
but that it has taken countless ages for the Sun and 
stars to attain their present state of evolution. It is 
shown that in the beginning the nebular condition 
prevailed, and the law of universal gravitation caused 
the matter to gather into masses called nebulae. 
The process then is the following : as these gaseous 
masses condense, there arises a motion of rotation 
around some centre, so that the nebula begins to 
rotate on an axis. The particles of the nebula are 
acted upon by two forces: (i) The gravitation of 
the mass; (2) The centrifugal force of rotation. 
As the mass condenses, the rotation becomes more 
rapid, owing to the conservation of the moment of 
momentum, and the contraction of the radius of 



The Cosmogony 243 

gyration ; so that at length the centrifugal force be- 
comes equal to gravity, and the particles on the 
equator of the mass cease to fall toward the centre. 
Thus a ring (or lump) of nebulous matter is left 




THE GREAT NEBULA IN ANDROMEDA 
{Photographed by Roberts, 1888 — Exposure ', four hours) 

behind, revolving around the central mass in an 
elliptic orbit, so well illustrated in the above engrav- 
ing of the great nebula in Andromeda. The body 
thus separated will in the course of ages condense 
into a satellite or planet, or double star, as observed 
in space. 



244 Stars and Telescopes 

Having stated this essential idea of celestial evo- 
lution, the history of the subject will now be briefly 
surveyed. Cosmogony has engaged the attention of 
philosophers from time immemorial ; but it is only 
in the last century and a half that substantial progress 
has been rendered possible by the general advance 
of all related sciences. Anaximander, Anaxagoras, 
Democritus and other ancient philosophers held that 
the world had arisen from the falling together of 
diffused matter in a state of chaos ; and proceeding 
on this supposition, they endeavored to predict its 
future career and ultimate destiny. Some of the 
Greek philosophers, Aristotle, for example, and 
Ptolemy, while admitting the perishable character of 
all terrestrial things, maintained that the world beyond 
the orbit of the Moon is imperishable and eternal. 
Other philosophers followed Anaximander and Anaxi- 
menes in maintaining that, as the world had arisen in 
time, so it would in time pass away ; and thus the 
universe had undergone and would continue to un- 
dergo alternate renewals and destructions. 

In like manner the still more ancient cosmogony 
of Genesis declares that in the beginning the Earth 
was ' without form and void, ' and implies that the visi- 
ble world has arisen by a process of gradual evolution. 
These theories of the ancients are of course mere 
speculations supported by broad analogies of nature, 
but as they are in general accord with modern results, 
they are of interest in the history of the cosmogony. 

Cosmogonic speculation of a scientific character 
began with Kant, who was the first of modern phi- 
losophers to advance a definite mechanical explana- 
tion of the formation of the heavenly bodies, and par- 
ticularly of the bodies composing the solar system. 



The Cosmogony 245 

The views of Kant, however, do not seem to have 
received much scientific recognition until after La 
Place's independent formulation of the nebular hy- 




Immanuel Kant (1724-1804) 

pothesis. La Place advanced the nebular hypothesis 
as a result of his prolonged study of the mechanics 
of our system, and the sound dynamical conceptions 
underlying his explanation secured for it immediate 
recognition. The work of Sir William Herschel 
lent observational support to La Place's ideas, and 
the observations of Sir John Herschel strengthened 
the evidence gathered by his illustrious father. 

But about 1850, when Lord Rosse's great reflector 



246 



Stars and Telescopes 




La Place (i 749-1 827) 

showed the discontinuous nature of some of the objects 
then classed as nebulae, the question arose whether 
with sufficient power all nebulae might not be re- 
solved into discrete stars. Fortunately, the inven- 
tion of the spectroscope by Kirchhoff about i860, 
and D r Huggins's application of it to the heavenly 
bodies at once answered this question in the negative, 
by showing that many of the nebulae are masses of 
glowing gas in the process of condensation. It then 
became a matter of great scientific interest to inves- 
tigate the formation of the heavenly bodies. The 



The Cosmogony 



247 



principle of the conservation of energy and the me- 
chanical theory of heat, which von Helmholtz was 



p 




LORD ROSSE'S GREAT SIX-FOOT REFLECTING TELESCOPE 
(Birr Castle. Parsonstown, Ireland) 



the first to apply to the nebular contraction of the 
Sun, and Lane's researches on condensing gaseous 



248 



Stars and Telescopes 



masses, together with the researches of Lord Kelvin 
on the Sun's age and heat, have each marked im- 
portant epochs in the development and confirmation 
of the nebular hypothesis, as now maintained and 
generally accepted by astronomers. The importance 
of Lane's work consisted in showing that a gaseous 
mass condensing under its own gravitation might rise 
in temperature, and thus La Place's assumption of an 
original high tempera- 
ture became unneces- M 
sary, as the heat might 
be developed by the fall- 
ing together of cold 
matter. La Place sup- 
posed that the planets 
and satellites resulted 
from the condensation 
of rings which were suc- 
cessively shed by the 
contracting nebula, but 
to explain how a ring 
would become a planet 
has always been some- 
what difficult. Yet prior 
to the researches of Professor G. H. Darwin, the ( ring- 
theory' was never seriously questioned, at least in 
regard to planetary evolution. But the course of 
thought was greatly changed when he showed that the 
Moon probably separated from the Earth not in the 
annular form supposed by La Place, but in the form 
of a globular mass, which had been driven away to its 
present distance by the tidal reaction of the Earth. 
The tides here alluded to are not surface oceanic tides, 
but tides in the body of the molten globe, which were 




LORD ROSSE (180O-1867) 



The Cosmogony 249 

especially high when the two bodies were close to- 
gether. As the matter composing our planet is fac- 
tional, the tides lag, and the tidal protuberance in 
the Earth therefore points in advance of the Moon, 
and exerts on it a small force tending to accelerate 
its motion, with the result that the distance increases ; 
while the reaction of the Moon against the protube- 
rance retards the rotation of our globe on its axis. 

In this way Professor Darwin explains the expan- 
sion of the Moon's orbit from age to age, and shows 
that the working of tidal friction would also render it 
more and more eccentric. Also he sought to apply 
this remarkable theory to the development of the 
planetary system as a whole, but it was found that 
elsewhere in our system the effects ot tidal friction 
had been comparatively unimportant. 

The general result of Professor Darwin's work on 
the cosmogony of the solar system is to leave La 
Place's theory without any material change except 
in the system of Earth and Moon. If it were possi- 
ble to overcome the mathematical difficulty of ex- 
plaining how a ring could condense into a planet, the 
regularity in the motions of the planets and satellites 
and the circularity of their orbits might be explained. 
The too rapid revolution of the satellite Phobos round 
the planet Mars can be accounted for as a result of 
tidal friction ; but it is difficult to explain in a satisfac- 
tory manner the retrograde motion of the satellites 
of Uranus and Neptune, though the suggestions of M. 
Faye are ingenious and possibly of lasting value. 

Recently D r T. J. J. See, of the University of Chi- 
cago, has taken a farther and very important step in 
the development of the theory of cosmical evolution, 
and incidentally he has applied it to the planetary 



250 



Stars and Telescopes 



system. In investigating the origin of double stars, 
he found that their orbits are generally very eccen- 
tric, as compared with the orbits of the planets and 
satellites, and it occurred to him that the cause of 
this remarkable phenomenon might be the secular 
action of tidal fric- 
tion. His orbit of 
a Centauri shown 
here is a typical bi- 
nary with about the 
average eccentri- 
city. 

It appears that 
double stars have 
arisen from the 
breaking up of dou- 
ble nebulae by a 
process of division 
resembling fission 
among the proto- 
zoans, and that their 
orbits were origin- 
ally nearly circular. 
According to D'See 
the average eccen- 
tricity is about 0.45, 
while in the plane- 
tary system the ave- 
rage eccentricity is 
only 0.0389, or one twelfth of that found among bi- 
nary stars. Another very important point in his 
researches lies in the connection pointed out between 
double nebulae and the dumb-bell-shaped figures of 
equilibrium discovered by Darwin and Poincare. 




ORBIT OF ALPHA CENTAURI 
{Computed and projected by D r See) 



The Cosmogony 251 

These eminent mathematicians have substantially 
proved that it is possible for a rotating nebula to 
break up, under its own contraction, into an hour- 
glass figure exactly resembling the double nebulae ob- 
served in space. On these pages are reproduced the 
figure of Poincare, and a typical double nebula, to 
show the process of division. 

The masses resulting from the figures of Darwin 
and Poincare are much too large relatively to render 

the results applicable 
to our own system, 
where the attendant 
bodies are always 
very small. Just such 
masses, however, ex- 
ist among double 
nebulae and double 
stars ; and D r See 
therefore concludes 
that if such large rel- 
ative masses are not 

TYPICAL DOUBLE NEBULA IN VIRGO found in OUr SVSteiTl 

,„ - c t xj » r 4 ; x they are found in 

(No 1202 in Sir John Herschel s Catalogue) J 

{No. 61 in messier's Catalogue) abundance elsewhere 

in space. He points 
out that the double stars are remarkable for two 
fundamental facts: (1) The large mass- ratios of the 
components, so that the masses are often nearly 
equal and always comparable; and (2) the high 
eccentricities of their orbits. 

Among all known systems, that of the Sun is re- 
markable for the great number and small masses of 
the attendant bodies, and for the near approach to 
circularity in the orbits. Nearly all the mass of the 





252 Stars and Telescopes 

original solar nebula is embraced in the Sun, which 
has 750 times the mass of all the attendant planets 
and satellites com- 
bined. Our system is 
essentially single — all 
the mass in the Sun 
— while in binary stars 
the systems are essen- 
tially double. 

Applying the law of 
binary evolution to 
the planetary system, the figure of poincare 

D r See concludes that 

the planets were separated not in the form of rings, 
as La Place supposed, but in the form of lumps or 
masses, which would easily condense into planets and 
satellites. In this manner he escapes the necessity 
of explaining how rings would condense into single 
masses ; indeed, he maintains that rings would not 
condense at all, but become swarms of small bodies, 
like those which make up the rings of Saturn and 
the small planets between Mars and Jupiter. 

It is still too early to pronounce an opinion as to 
the ultimate value of these later researches in cos- 
mogony. The weak point in the older theories lies 
in the deduction of all cosmical laws from our own 
system, whose formation appears to have been some- 
what anomalous. But as D r See's theory of cosmical 
evolution has been deduced from the study of other 
systems in space, and is in harmony with the known 
facts of Nature, it may fairly be regarded as the 
most advanced step yet taken in the science of the 
formation of the heavenly bodies. 



The Cosmogony 253 

Kepler, Epitome Astronomiae Copernicanae (Frankfort 1635). 
Swedenborg, De Chao Universal* Solis et Pianetarum (1734, 

and London 1845). 
Wright, A New Hypothesis of the Universe (London 1750). 
1 Kant, Naturgeschichte unci Theorie des Himmels (Konigsberg 

1755). 
Lambert, Cosmologische Brief e die Einrichtung des Weltbaues 

(Augsburg 1 761). 
Herschel, ' Nature and Construction of Sun and Fixed Stars,' 

Philosophical Transactions for 1795. 
La Place. Exposition die Systeme die Monde (Paris 1796) ; and 

Annuaire du Bureau des Longitudes for 1867. 
Comte, ' Cosmogonie Positive,' U Lnstitut, iii. (1835), 31. 
Mayer, Dynamik des Himmels (Heilbron 1848). 
Rankine, ' Reconcentration of the Mechanical Energy of the 

Universe,' Philosophical Magazine, iv. (1852), 358. 
Thomson, Mechanical Energies of the Solar System (Edinburgh 

1854)- 

Kirkwood, 'On the Nebular Hypothesis,' Am, Jour. Science, 

xxx. (i860), 161. 
Trowbridge, ' On the Nebular Hypothesis/ several papers m 

American Journal of Science for 1864 and 1865. 
Proctor, ' La Place's Nebular Theory/ in his Saturn and its 

System (London 1865), 201. 
Roche ; La Constitution et VOrigine du Systeme Solaire (Mont- 

pellier 1875). 
Nyren, ' Ueber die von Emanuel Swedenborg aufgestellte 

Kosmogonie/ Viertel. Astron. GeselL, xiv. (1879), 80. 
Clifford, 'The First and the Last Catastrophe/ in his Lec- 
tures and Essays, i. (London 1879). 
Peirce, 'Cosmogony/ and 'From Nebula to Star/ in his 

Ldeality in the Physical Sciences (Boston 1881). 
Darwin, Papers in Proceedings and Philosophical Transactions 

Royal Society, 1 878-1 881. 
Helmholtz, 'On the Origin of the Planetary System/ Popular 

Lectures, 2d series (New York 1881). 
Newcomb, ' The Cosmogony/ in his Popular Astronomy (New 

York 1885), 503. 
Faye, Sur VOrigine du Monde (Paris 1885). 
Faye, ' Sur la Formation de l'Univers et du Monde Solaire/ 

Annuaire du Bureau des Longitudes for 1885. 
Wolf, Les Hypotheses Cosmogoniques (Paris 1886). 



254 Stars and Telescopes 

Parkes, Unfinished Worlds (New York 1887). 

Braun, Ueber Cosmogonie vom Standpunkt Christlicher Wissen- 
j^/? (Minister 1887) ; Clerke, Nature, xxxviii. (1888), 365. 

Janssen, * L'Age des Etoiles,' Annuaire die Bureau des Longi- 
tudes for 1888. 

Coakley, 'On the Nebular Hypothesis of La Place/ Papers 
American Astrono?nical Society (Brooklyn 1888). 

Croll, Stellar Evolution (New York 1889). 

HlRN, Constitutio?i de V Espace Celeste (Paris 1889). 

Ball, Time and Tide (London and New York 18S9). 

Lockyer, The Meteoritic Hypothesis (London 1890). 

Green, The Birth and Growth of Worlds (London 1890), 
Bibliography. 

Tuckerman, ' References to Thermodynamics,' Smithson. Misc. 
Collections, No. 741 (1890). 

Klein, Kosmologische Brief e (Leipzig 1891). 

Keeler, Astronomy and Astro-Physics, xi. (1892), 567, 768. 

Clerke, The System of the Stars (New York 1892). 

Darwin, ' Cosmogonie Speculations founded on Tidal Fric- 
tion,' Article ' Tides,' Encyclopaedia Britannica (9th ed.), 1892. 

Gore, The Visible Universe (London and New York 1893). 

See, Die Entivickelung der Doppelstern-Systenie (Berlin 1893). 

Ball, The Story of the Heave?is, Chapter xxvii. (London 1S93), 

Stanley, Notes on the Nebular Theory (London 1895). 

Lockyer, Evolution of the Heavens and the Earth (London 1895). 

Nolan, Satellite Evolution (Melbourne 1895). 

See, Researches on the Evolution of Stellar Systems (Lynn 1896). 

Gerland, in Valenttner's Handworterbuch der Astrono?nie 
(Breslau 1897). 

See, The Atlantic Monthly, lxxx. (1897), 484. 

LlGONDES, Formation Mecanique du Systeme du Monde (Paris 
1897). 

Chamberlin, ' Climatic Changes,yiwr. of Geology, v. (1897), 653. 

MouLTON, Popular Astronomy, v. (1898), 508. 

La Fouge, Formation du Systeme Solaire (Chalons-sur-Marne 
1898). 

Darwin, The Tides and Kindred Phenomena in the Solar 
System (Boston 1898). 
Consult also under Nebula* the references in Poole's Indexes 

cited on page 315 of this volume. Also in The Westminster 

Review (July 1858) is an able discussion by Herbert Spencer. 

Matson's References for Literary Workers (Chicago 1892) con- 
tains at pp. 388-9 a bibliography of popular articles.— D.P. T. 



CHAPTER XVII 

THE FIXED STARS 

IT remains to give a short account of the motions 
and distances of those far more remote heavenly 
bodies which come under the general designation of 
fixed stars, devoting also a few words to the investi- 
gations concerning the probable motion of our own 
•system, as a whole, among them. 

Those fixed stars which are bright enough to be 
visible to the naked eye have been watched from the 
most remote antiquity ; but, excepting the changes of 
brightness to which a few are subject, and the occa- 
sional appearance of a temporary star never seen 
"before, no other knowledge of the fixed stars than 
that of their comparative brightness and apparent 
distribution in the sky was obtained before the inven- 
tion of the telescope, or indeed could be. With 
regard to the temporary stars, it is not in all cases 
easy to say whether the accounts handed down to us 
really refer to a new star or to a comet. The most 
ancient record of such an object relates that in b. c. 
134, a new star burst out with a brightness sufficient to 
Tender it visible in the day-time, and attracted the 
attention of Hipparchus, leading him to draw up a 
catalogue of stars (the first ever made), with a view 
of enabling future ages to trace with certainty any sub- 
sequent appearances or disappearances. The Chi- 
nese annals show that the astronomers of that country 



256 



Stars and Telescopes 



also noticed this star, which seems to have been situate 
in the southern hemisphere and in the constellation 
Scorpio. They also speak of one said to have been 
seen in the constellation Centaurus in a year corre- 
sponding to a. d. 1 73. 52 



52 Cataloguing the stars is the most tedious labor of the mod- 
ern practical astronomer. A high degree of accuracy in the 
positions is demanded, and the latest catalogues embrace many 
thousand faint stars, most of them invisible to the naked eye- 
Stellar catalogues nearly always contain the magnitudes of the 
stars, given according to an arbitrary scale of numbers express- 
ing their brightness. Twenty of the brightest stars of the fir- 
mament, ten in the northern celestial hemisphere and ten in 
the southern, are rated of the first magnitude. Then follow 
about 

65 of the second magnitude, 
200 of the third, 
500 of the fourth, 
1400 of the fifth, 
5000 of the sixth, 

these last being so faint that they 
are just visible to a keen eye on- 
clear moonless nights. The num- 
ber increases rapidly with each 
fainter magnitude, nearly in geo- 
metric proportion; so that, if we 
include stars of the tenth magni- 
tude, the faintest included in cata- 
logues, there are about a million in 
all. Estimates of the uncounted 
hosts of uncatalogued stars still 
fainter and fainter, down to the 
17th magnitude, make the total 
number far in excess of 100 mil- 
lions. Professor Barnard's fine 
photograph opposite shows how thickly they are strewn irk 
many parts of the celestial vault. Until recent years the 
magnitudes of the brighter stars were for the most part deter- 
mined by mere eye estimates, and Heis, the German astrono- 
mer, who spent many years observing paths of meteors, was- 




heis (1806-1877) 




MILKY WAY IN SAGITTARIUS (R. A. = l8 h IO m . DECL. = S. 20°) 
(Photographed by Professor Barnard at the Lick Observatory. Exposure, \\ hours) 



258 



Stars and Telescopes 



Another star, as bright at one time as the planet 
Venus, is said to have appeared in the year a. d. 389 

an exceedingly accurate observer of stellar magnitudes as well. 
But the most precise results have been obtained by means of 
instruments called photometers, in which every star is re- 
peatedly compared with a standard light of known intensity. 




THE MERIDIAN PHOTOMETER OF HARVARD COLLEGE OBSERVATORY 

{Devised by Professor Edward C. Pickering, and used under his direction in 

determifiing the magnitude of all the bright stars in the entire sky) 



Stellar photometers are of varied designs. Pritchard used 
a so-called wedge photometer, in which a thin strip of colored 
glass, with faces slightly divergent, was attached to the eye- 
piece, and that position of the glass wedge was recorded at 



The Fixed Stars 



^59 



(in the reign of the Emperor Theodosius) : but from 
the accounts given by the ecclesiastical historians, it is 

which the star's light was extinguished. Professor Pickering 
has successfully employed a type of his own devising, and 
named the meridian photometer, shown opposite, and so 
called because each star, when near the meridian, is directly 
compared with Polaris, itself an invariable standard. The 
oblique mirrors enable this to be done, no matter what the 




PHOTOGRAPHIC EQUATORIAL TELESCOPE 

(Built by Sir Howard Grubb for the Royal Observatory at 
Cape Town. The lower tube is the photographic telescope ; 
with a \yinch object-glass; the tipper one is an optical or 
guiding telescope -with a 9- inch objective. The tubes are 12 
feet long. Similar instruments by the same maker, for the 
Iyitemational Astrographic Survey, are moimted at Green- 
wich, Oxford, Melbourney Sydney, and Tacubaya, in Mexico) 



260 Stars and Telescopes 

evident that a remarkable comet was seen at the time 
to which this appearance is referred, so there can be 

altitude of the star. With this instrument, as mounted at 
Cambridge, Massachusetts, and later at Arequipa, Peru, the 
magnitudes of all the brighter stars of both northern and 
southern hemispheres have been determined with a degree of 
accuracy unsurpassed. Attempts have been made in the hope 
of increased precision in magnitude by means of photography, 
but as yet without much encouragement. Photography, how- 
ever, has already revolutionized the construction of star cata- 
logues, because the highly sensitive plate records in an hour 
as many stars as an astronomer could observe the position of 
in many weeks. Foremost in these highly significant re- 
searches is D r David Gill, the earliest to propose an interna- 
tional congress of astronomers, which first met at Paris in 1887, 
and undertook an astrographic survey and photographic map of 
the entire heavens. This is now in progress, with 18 instruments 
like the one on page 259, six of which are located in the south- 
ern hemisphere. Nearly all the great nations originally joined 
in this important work, including the observatories at Paris, 
Algiers, Bordeaux, Toulouse ; San Fernando (Spain), Catania, 
and Rome (Vatican) ; La Plata, Rio de Janeiro, and San- 
tiago, in South America; Helsingfors and Potsdam in Ger- 
many; in addition to the observatories named on the preceding 
page. Some, however, have dropped out, from lack of funds. 
The total number of plates exposed at the conclusion of this 
comprehensive survey will be more than 20,000, and the total 
expense for all nations will aggregate not far from $100 for 
each plate. Then the plates must be carefully measured, and 
the resulting data converted into arcs of the celestial sphere, 
so that the right ascension and declination of every star may 
be given as in catalogues constructed in the old-fashioned way 
by means of the meridian circle (see page 368). D r Kapteyn 
of Groningen is foremost in the work of deriving star-positions 
from photographs, and he has already measured and catalogued 
nearly half a million stars from the Cape Town plates. At 
Paris the work is progressing rapidly under the direction of 
M ,le Klumpke. But the degree of precision attainable by the 
photographic method does not displace the necessity for the 
labors of the astronomer with the telescope alone. The long- 
tested methods of slow observation with meridian instruments 



The Fixed Stars 



261 



little doubt that this report of a new star is simply 
due to a misunderstanding of the description of the 

must still be employed when the last degree of precision is 
sought. The name of Argelander, a pupil of the great 
Bessel, stands out pre-eminently for persistent faithfulness in 




F. W. A. ARGELANDER (1799-1875) 



this class of observation. His famous Durchmusterung of the 
northern heavens embraces no less than 324,198 stars, set down 
with some precision, both in catalogues and in a series of stellar 
charts, which are a prime essential in all working observatories. 
In 1865 the Astronomische Gesellschaft of Germany undertook 



262 



Stars and Telescopes 



comet, which moved in the heavens from near the 
place where Venus then was to the constellation Ursa 

a supplementary work of vast magnitude, the re-observation of 
about one third of Argelander's stars, with the highest degree 
of accuracy attainable. These Gesellschaft zones, observed at 
13 observatories, European and American, are now nearly com- 
plete. What Argelander did for the northern sky, Gouli> 




BENJAMIN APTHORP GOULD (1824-1896) 

did for the southern heavens, by residing for fifteen years at 
Cordoba, Argentine Republic. Together with his assistants, he 
observed nearly 75,000 stars, extending to the 9^ magnitude; 
published in 1879 tne Uranometria Argentina, an elaborate 
series of charts of the southern heavens ; in 1886 the Argentine 
General Catalogue of 32,000 stars ; and in 1897, shortly after his 
lamented and accidental death, D r Chandler brought out the 
last great work of Gould, being a complete discussion of about 
40 clusters of stars in the southern sky, with positions derived 



The Fixed Stars 263 

Major. A similar remark applies to new stars which 
are said to have appeared in the northern heavens in 
a. d. 945 and 1264. In all probability both were 
comets : in the latter year (that of the battle of Lewes) 
a splendid comet is known to have been seen. 

But it is quite certain that a very conspicuous and 
remarkable new star did appear near the constellation 
Cassiopeia in 1572. It was noticed in other parts of 
Europe several days before it was seen by Tycho 
Brahe ; but he made a series of careful observations 
of the star, and left an elaborate account of it. He 
first saw it while residing at his uncle's house in Scania 
(then included in the kingdom of Denmark, but united 
to the rest of Sweden in the following century), on 1 ith 
November 1572. Its brightness even then rivalling 
Sirius, and increasing until it surpassed that of Jupiter, 
the star was for a short time visible in broad daylight ; 
but it soon began gradually to fade away, and by March 
1574 had totally disappeared, after having been seen, 
with more or less brilliancy, during a period of about 
16 months. 

from measurements upon photographs, which Gould began at 
Cordoba in 1872 as the pioneer. In 1889 Miss Catherine 
W. Bruce of New York donated to Harvard College Obser- 
vatory the sum of $50,000 for a great photographic telescope, 
•of 24 inches aperture. This has been constructed by Alvan 
Clark & Sons, from designs by Professor Pickering, and it 
is now mounted in Peru, where the more interesting regions of 
the southern heavens are in process of permanent record. This 
telescope and its unusual type of mounting are illustrated on 
page 264, and opposite is a reproduction of a part of one of the 
star charts taken with it. On the entire original glass, 14 X 17 
inches square, were 400,000 stars by actual count. Probably 
the Bruce telescope is the most powerful optical instrument in 
•existence. Certainly it can photograph the faint glimmer of 
thousands of stars which no human eye can ever expect to see 
in any telescope. — D. P. T. 




o 
u 

W 

w 

H 



u 







;<> 



»t-»>-*r. 




I 
I 



VICINITY OF ETA CARINAE (ARGUS) R. A. IO h 4I m , DECL. 5Q°S. 

{Photographed by Professor Bailey with the Bruce telescope, exposure 4 hours) 

[_E ngraving from Todd's * New Astronomy? by special permission of tlie American Book 

Company, Publishers] 



266 Stars and Telescopes 

Another temporary star appeared in the right foot 
of the constellation Ophiuchus in the year 1604, and 
was observed by Kepler and others. At one time as 
bright as Venus, it continued visible for more than a 
year, disappearing about the end of 1605. On 20th 
June 1670 Father Anthelme, a French Carthusian of 
Dijon, noticed another new star of the third magni- 
tude, very near the head of Cygnus. Observed both 
by Hevelius and by Cassini, it underwent several 
remarkable changes in brightness during two years, 
then completely disappeared, and has not since been 
seen. Another star in the same constellation (now 
known as 34 Cygni) underwent some remarkable 
fluctuations of light in the 1 7th century, but has re- 
mained unchanged in brightness since, being just 
visible to the naked eye. 

Within the last fifty years several temporary stars 
have appeared quite suddenly, whose previous exist- 
ence is unrecorded. One of these was in 1848, when 
Hind noticed, on 28th April, a star of the fifth mag- 
nitude (easily visible to the naked eye), in a part 
of the constellation Ophiuchus, where he was certain 
that, so recently as the 5th of that month, no star so 
bright as the ninth magnitude was visible; nor is 
there any record of a star having been observed there 
at any previous time. From the date of its discovery 
it began continuously to diminish in brightness, and it 
is now visible only through very powerful telescopes. 
A still more remarkable, as well as more recent case of 
the appearance of a temporary star (temporary at least 
as regards its visibility to the naked eye) is that of a 
star in the constellation Corona Borealis, which seems 
to have burst out quite suddenly, 12th May 1866, when 
it was first noticed by Birmingham in Ireland. Of the 



The Fixed Stars 267 

second magnitude at the time of discovery, it dimin- 
ished so rapidly as to be invisible to the naked eye 
by the end of the month. In the autumn of the same 
year it increased somewhat in brightness again, — but 
not sufficiently to become visible without a telescope, — 
and afterward sank down to what must be considered 
its normal brightness. A third instance of the kind 
occurred in 1876, when Schmidt, of Athens, noticed 
on 24th November, a new star of the third magnitude 
in the constellation Cygnus, which afterward gradually 
faded away, ceasing to be visible to the naked eye in 
about a month, and is now to be seen only with the 
aid of a very powerful telescope. Toward the end of 
August 1885 another new star appeared in the midst of 
the great nebula in Andromeda ; but it never became 
bright enough to be visible to the naked eye. The 
most recent case is that of a star in Auriga, which was 
first noticed at the end of January 1892, but was after- 
ward found to have been registered by photography 
in the preceding December. It faded away in March 
1892, after having been for a few weeks visible to the 
naked eye. 53 

53 Nova Aurigae has the most singular history of all the 
temporary stars. D r Anderson, an amateur of Edinburgh, 
was its first discoverer, his meagre equipment consisting of only 
a star atlas and a pocket telescope magnifying ten times. But 
•examination of the Harvard stellar photographs at once 
showed that the star had many times been recorded by its 
own light on plates exposed between ioth December 1891 and 
20th January 1892. Measures of them showed that Nova 
Aurigae had rapidly attained its maximum brightness unob- 
served on 20th December, when it was of the 4.4 magnitude, 
and therefore plainly visible without a telescope. By the 1st 
of April the star had become invisible, except with a very 
large telescope, but in August 1892 a temporary brightening 
brought its magnitude up from the 13th to the 10th. Through 



268 Stars and Telescopes 

The above are special cases, but the number of 
stars which may be called regularly variable, being 

1S93 aR d J 894 it remained between the roth and nth magni- 
tude, and Professor Barnard's observations with the 36-inch 
Lick telescope from 1892 to 1895 sn ° w tna t Nova Aurigae had 
become a small, bright nebula with a star-like nucleus. Pro- 
fessor Campbell, D r von Gothard and others, who critically 
examined the star's spectrum, showed that it was practically 
identical with the spectra of planetary nebulae. Parallax 
observations, similar to those described later in this chapter r 
showed that the star was as remote from the solar system as 
the average of the stars whose distances are known. The 
outburst which produced the sudden rise in its brightness 
must, therefore, have taken place on a scale inconceivably 
grand. Just what caused it cannot be said to be known ; but 
the complex character of the star's spectrum in February 1892 
indicates a probable collision, or at least a near approach, of 
two vast gaseous bodies travelling through interstellar space, 
with a relative motion exceeding 500 miles a second. 

A swarm of meteorites swiftly traversing a remote gaseous 
nebula would account for most of the peculiarities of the 
spectrum of Nova Aurigae. But a wholly satisfactory theory 
is not likely until many other new stars appear in the sky, and 
their constitutions are studied by means of spectra photo- 
graphed at short intervals. That lynx-eyed watch of the whole 
sky, both northern and southern, now kept by means of pho- 
tography, enables us to say that new stars are not infrequent 
objects, as formerly supposed. M rs Fleming in 1893 found 
one of the seventh magnitude in the southern constellation 
Norma, with a spectrum practically identical with that of Nova 
Aurigae (indicating hydrogen and calcium), and which is now 
nebular also. And the same keen observer has since found 
many other objects of this highly interesting character, the 
most noticeable of which appeared in 1895 m Carina, a part 
of the w r ide southern constellation Argo. Nova Carinae fell 
in three months from the eighth magnitude to the nth, and 
exhibited all the essential features of the new stars in Norma 
and Auriga. Still another was found by her the same year 
in Centaurus, which had a spectrum different from its prede- 
cessors, but like them eventually became a gaseous nebula. 
It is significant that nearly all the Novae have gleamed in or 



The Fixed Stars 269 

subject to regular changes in brightness of various 
degrees, is at present known to be very large, and is 
from time to time increased by fresh discoveries. 
Usually these are subject only to smaller mutations of 
brightness. Of the few stars which undergo remark- 
able irregularities of this kind, the two most interesting 
cases are o Ceti and rj Argus. The former, sometimes 
called Mira Ceti, was first noticed as being subject to 
change in 1596, by David Fabricius, who saw it of the 
third magnitude in August, and perceived in October 
that it had ceased to be 
visible. Bayer saw it in 
1603, and Phocylides in 
1638, the latter noticing 
(which Bayer did not) that 
it was the same star, thus 
shown to be variable in 
brightness. The observa- 
tions of Hevelius between 
1648 and 1662 established (J . F . w. Herschel) 

its period, which is about 

331 days in length; but the changes of brightness 
during this interval are themselves of a very variable 
kind, nor is the period quite constant in length. The 
star is usually visible to the naked eye for about six 
months, and invisible during the succeeding five. 

Halley was the first to suspect changes of bright- 
ness in that remarkable star in the southern hemi- 
sphere, r) Argus, which he had observed at Saint Helena 

near the Milky Way ; and in the case of Nova Aurigae at least, 
the striking display of 1892 must really have taken place as 
long ago as the beginning of the 19th century. In the latter 
part of 1898, a star-like condensation was reported in the centre 
of the nebula in Andromeda. — D. P. T. 




zyo 



Stars and Telescopes 



in 1 6 7 7 as of the fourth magnitude. Lacaille in 1 75 1 
saw it of the second \ and its changes from time to 
time since have been exceedingly irregular. In 1838, 
and again in 1843, it surpassed for a while all other 
stars in brightness, excepting only Sirius. After the 
latter date, it slowly but steadily diminished, and 
ceased to be visible to the naked eye in 1867, an d 

it so remains, though its 
brightness has slightly in- 
creased in the last few 
years. 

Of the variable stars 
of short period, the most 
remarkable is Algol or £ 
Persei. Its usual magni- 
tude is about the second, 
and as such it shines 
constantly and regularly 
for a period of about 
two and a half days ; then 
it fades gradually almost 
down to the fourth mag- 
nitude, afterward recov- 
ering its ordinary brightness by a similar gradual in- 
crease. The whole amount of change takes place in 
about nine hours, so that the complete length of a 
period is not quite three days ; more accurately, 
2 d 2o h 48™ 5 5 s . 4. Spectroscopic observations have 
proved that these variations are caused by the regular 
interposition of an opaque body revolving round Algol, 
and cutting off at each revolution a portion of its light 
in the manner of a partial eclipse. 

The above are the most conspicuous and easily 
detected changes of brightness in the fixed stars ; but 




SCHONFELD (1828-1891) 



The Fixed Stars 



271 



about 150 stars are now known to be variable, and the 
application of photometry as an accurate means of 
measuring the amount of light of a star is constantly 
increasing this number. In many cases the variability 
is confined within narrow limits ; in others, the stars, 
even when at their greatest brightness, are scarcely, or 
not at all, visible to the naked eye. 54 

54 So rapid has been the recent progress in our knowledge 
of the variable stars that the total number now known embraces 
about 1,000, if we include the rather remarkable discoveries of 
Professor Bailey, who, beginning in 1896, has found about 
500 variables in the dense globular clusters photographed with 
the Harvard telescopes. Their changes of magnitude are 
marked within a few hours. In a> Centauri alone (the cluster 
shown on page 269) 125 variables were discovered. D r Chand- 
ler of Cambridge has published several catalogues of variables 
in which about 500 of these objects are carefully classified. 
They are distributed all the way round the heavens, and for 
the most part are included in a belt or zone tilted about 18 to 
the celestial equator. Variables are best observed by means 
of Father Hagen's excellent Atlas. Following are a few of 
the variables : — 

Variable Stars 



star's name 


Position for igoc 


).o 


VARIATION 














R. 


A. 


Decl. 


Period 


Range 




h 


m 





t 


d 




Omicron Ceti 


2 


H 


- 3 


26 


33 1 


1.7 to 9.5 


)8 Persei 


3 


2 


+40 


34 


A 


2.3 to 3.5 


£ Geminorum 


6 


s» 


+20 


43 


ID* 


3-7 to 4.5 


R Leonis 


9 


42 


+11 


S4 


3 T 3 


5.2 to 10 


8 Librae 


14 


S6 


- 8 


7 


2±- 


5 to 6 2 


a Herculis 


17 


IO 


+14 


30 


90+ 


3.1 to 3 9 


X Sagittarii 


17 


41 


-27 


48 


7 


4 to 6 


£ Lyrae 


18 


46 


+33 


"5 


™i 


3.4 to 4.5 


5 Cephei 


22 


25 


+57 


54 


Si 


3.7 to 4.9 



Many of the newly discovered variables being faint stars, 
they have no regular name except their number in some cata- 
logue of positions. They are, therefore, designated by the 



2.J2 Stars and Telescopes 

The determination of the parallaxes, and thereby 
the distances of the fixed stars, constitutes a problem 
which completely baffled astronomers until little more 
than fifty years ago ; for so vast is the distance of 
these bodies, that, although we use the diameter of 
the Earth's orbit as a base, by comparing observations 
made at opposite parts of the year, nevertheless the 
angle at the star subtended by this diameter is gener- 
ally so small as to be scarcely distinguishable from 
inevitable errors of observation. The half of this angle 
is the star's annual or heliocentric parallax. 

Early in the present century Brinkley thought his 
observations at Dublin indicated that he had found 



letters R, S, T, and so on, in the constellation to which they 
belong. The number of variables of the iUgol type is now 
about 20, two of the most pronounced being U Cephei and W 
Delphini, and the total variation in the magnitude of each is 
about 2.5. W Delphini is never visible to the naked eye, but 
remains for about four days at its full brightness of about the 
9th magnitude, when in seven hours it falls to the 12th magni- 
tude, so that a 5-inch telescope will barely show it. Algol, the 
type star, is best visible in the northeastern heavens in the 
evenings of early autumn, and nearly overhead in winter. 
The minima are given in many almanacs, and such astronomi- 
cal journals as The Observatory and Popular Astroriomy. Its 
full decline takes place in rather more than four hours, and it 
pauses at minimum brightness only 15 or 20 minutes. Vari- 
ables are differently classified by various investigators, and 
Schonfeld of Bonn (page 270), a pupil of Argelander, de- 
voted much time to these puzzling bodies in his best years. 
Many variables are quite anomalous in their fluctuations, 
having no regular period, and still others present several 
mutations of brightness in every complete period ; as, for in- 
stance, j8 Lyrae, whose complex spectrum shows a wealth of 
helium bands and hydrogen lines not yet unravelled. The 
shortest known variable is o> Centauri 91, whose period is 
6 h 1 i m ; and other variables in this interesting cluster exhibit 
many exceptional peculiarities. — D. P. T. 



The Fixed Stars 273 

parallaxes amounting to 2" or 3" for several of the 
brighter stars \ but Pond (who succeeded Maskelyne 
as Astronomer Royal in 181 1) showed by more accu- 
rate Greenwich observations that these conclusions 
were untenable. The first really satisfactory determi- 




FRIEDRICH WILHELM BESSEL (1784-1846) 

nation was made long afterward by Bessel, in the case 
of a star only just visible to the naked eye, known as 
61 Cygni. Attention was directed to it as being prob- 
ably much nearer us than others, in consequence of 
its unusually large proper motion in the heavens, which 
s & t — 18 



274 



Stars and Telescopes 



carries it though an arc of about 5" every year. 61 
Cygni is itself double ; and taking advantage of the 
circumstance that there are two other small stars ia 
its close neighborhood (which, not sharing in this 
motion, are probably much farther off), Bessel, in 
1837, began observations at Konigsberg, with the 
view of determining the parallax of this star relatively 

to the small objects in the 
same field. As their paral- 
lax might fairly be consid- 
ered insensible, the result 
would practically be the 
parallax of 61 Cygni, or of 
the two stars composing it. 
In 1840 he was able to 
announce that this quantity 
was measurable, amounting 
to about o".35, a value 
which later observations by 
other astronomers have es- 
sentially confirmed. The re- 
sulting distance of 6 1 Cygni 
from the solar system is 
of miles. Beginning with 
those of Henderson (made about the same time as 
Bessel's of 61 Cygni), observations of a bright star in 
the southern hemisphere, a Centauri, show that its 
parallax is the greatest of all the fixed stars yet meas- 
ured ; and the best determination, made by D r Gill 
and D r Elkin at the Cape of Good Hope in 1881— 
83, amounts to o".75, indicating a distance equal to 
about 25,000,000,000,000 of miles. Several other 
stellar parallaxes have since been measured : that of 
Sirius is o ;/ .38 ; one small star in Lalande's catalogue 




C A. F. PETERS (1806-1880) 



over 50,000,000,000,000 



The Fixed Stars 



275 




BRUNNOW (182I-1891) 



(No. 21,185) nas yi^ded a parallax of about 0^.5, 
and that of another (No. 21,258) is about 0":$. Also 
many, smaller in amount, have been determined. Only 
by the rapid propagation of light is it possible to 
express the distances of the 
enormously remote fixed 
stars in small figures. In 
a year light travels nearly 
6,000,000,000,000 of 
miles ; and this inconceiv- 
able distance, now gener- 
ally adopted as the unit of 
length in expressing stellar 
distances, is termed a ' light 
year/ Of a Centauri, for 
example, it is customary 
to say that its distance is 
about 4J light years, and in like manner the distance 
of 6 1 Cygni is about seven light years. 55 

65 Stellar distances tax to the utmost the skill and patience 
of the practical astronomer. So minute are the quantities to 
be measured and calculated that finding a star's distance may 
be likened to the problem which would confront a prisoner 
who possessed instruments of the utmost precision, and 
was told to measure the distance of a mountain twenty miles 
away, but was given liberty only to observe the mountain from 
the window of his cell. In this case, the orbit of the Earth, 
186,000,000 miles across, would be represented by the largest 
hoop he could place in the window; while our globe itself, 
on the same scale, would shrink to a speck requiring a micro- 
scope to render it visible. The steadiest atmosphere, instru- 
ments of perfect type and construction, and observers of 
consummate training can alone cope with the obstacles 
encountered at every step. Following Bessel came the 
painstaking Peters, who, about the middle of the 19th cen- 
tury, attempted the more difficult undertaking of ascertaining, 
not the relative, but the absolute parallaxes of certain fixed 



276 Stars and Telescopes 



In speaking of 6 1 Cygni, the expression l double 
ir ' was used, and it is essential to distinguish between 



stars, among them Polaris, Capella, Arcturus, and Vega. His 
method employed the meridian circle (page 368) by which he 
was skilful enough to detect very delicate changes in the ap- 
parent direction of these stars with the change of season. 
About 1870 Brunnow, then Astronomer Royal for Ireland, 




Hugo gylden (1841-1896) 

began to devote his attention to these critical researches, de- 
termining many stellar parallaxes with high precision, and his 
work was ably continued at Dunsink for several years by Sir 
Robert Ball. Their measures were made with the microme- 
ter (page 343), and the mathematical formulae requisite in 
calculating such observations are presented in elegant form 
by Brunnow in his Handbook of Spherical Astronomy (Lon- 
don, 1865). Also Gylden (from 187 1 to 1896 Director of 
the Royal Observatory at Stockholm), and D r Auwers, of 




D r GILL S HELIOMETER AT CAPETOWN 

(Aperture, 6 inches. Built by Repsold of Hamburg in 1888, and chiefly used in deter- 
mining distance of Sun and stars. Instruments of this type in the hands of trained 
observers have given results of the highest precision yet reached in astronomical, 
measurement) 



278 



Stars and Telescopes 



the two classes of stars which come under that desig- 
nation. A stellar object which appears single to the 
naked eye, but when viewed with a telescope is seen 



Berlin, and D«- Otto Struve, late Director at Pulkowa (pp. 
130 and 133), have greatly advanced our knowledge of the dis- 
tances of the stars. But the favorite method at the present day 
is that originally employed by Bessel — measures by the heli- 
ometer, which is a telescope of medium size, mounted equatori- 
ally, as shown on page 277, and provided with a variety of 
intricate appliances for facilitating the astronomer's use of the 
instrument, and enhancing the accuracy of his measures with 
it. But the cardinal peculiarity of the heliometer is its divided 
object-glass, as in the opposite figure, one half of the glass 
being mounted in a sliding frame, which enables the observer 
to move it by a definite amount relatively to the stationary half. 
As each portion makes a perfect image in the field of view, any 
lateral displacement of the half-objective will produce a double 
image. In the case of the sun, the two images of his disk 
are then brought just tangent to each other; and so his diame- 
ter has been most accurately measured (heliometer meaning 
sun-measurer). The Yale Observatory possesses the only 
instrument of this type in America, mounted in 1882, and it 
has been successfully employed by D r Elkin in determining 
stellar parallaxes. Following is a table including many of the 
stars whose distances are best known : — 





Dl 


STANCES 


of Fixed Stars 










Position for 1900.0 




Distance in — 




Star's Name 

(In order of 

Distance) 


Magni- 
tude 




Paral- 
lax 






Proper 
motion 


R. A. 


Decl. 


Light- 
years 


Trillions 
of miles 


a Centauri 


— o.t 


h m 
14 33 


1 
— 60 25 


o-75 


4^ 


?5 


3-67 


61 Cygni 


5-i 


21 2 


+38 15 


o.45 


l\ 


43 


5.16 


Sirius 


— 1.4 


6 41 


—16 35 


0.38 


H 


5o 


*-3* 


Procyon 


0.5 


7 34 


+ 5 29 


0.27 


12 


7i 


1-25 


Altai'r 


0.9 


19 46 


+ 8 36 


0.20 


16 


94 


0.65 


o 2 Eridani 


4.4 


4 7 


~ 7 7 


0.19 


17 


100 


4-05 


Groomb. 1830 


6.5 


11 7 




-38 32 


0.13 


25 


147 


7-65 


Vega 


0.2 


18 34 




-38 41 


0.12 


27 


158 


0.36 


Aldebaran 


10 


4 3o 




-16 18 


O.IO 


32 


191 


0.19 


Capella 


0.1 


5 9 




-45 54 


0. 10 


32 


191 


o.43 


Polaris 


2.1 


1 23 




-88 46 


0.07 


47 


276 


0.05 


Arcturus 


0.2 


14 11 




-19 41 


0.02 


160 


95o 


2.00 



The Fixed Stars 279 

to consist of two so near as not to be separated by the 
unaided vision, is naturally called a double star. But 
the fact that there are two stars apparently in such 
close proximity does not of itself prove any connection 
between them ; they may, indeed, be merely optically 
double, that is, appearing double only because the 
individual stars happen to be nearly in the same line 
of sight, without reference to their actual distance. 
But Sir William Herschel's persevering survey of the 
heavens revealed to him so large a number of these 
apparently double stars that there was in many cases 
great probability of physical connection between the 





DIVIDED OBJECT-GLASS OF HELIOMETER 

{Giving single {Giving double 

image) image) 



Of all the stars whose distances have been measured, per- 
haps 50 are regarded as satisfactorily known, and many of 
them are shown approximately in the diagram on page 280, 
adapted from calculations by Raxyard and Gregory, in 
which the solar system is at the centre and the concentric 
circles are drawn at intervals of five light-years. Any star just 
outside the outer circle would have a parallax of o". 1. Within 
recent years photography has rendered great assistance in find- 
ing stellar parallaxes, chiefly because plates once exposed can 
be critically measured and re-measured at any time. The pho- 
tographs of Pritchard and Rutherfurd have contributed 
conspicuously to this desirable end. Gyld£n, from an inves- 
tigation of the parallaxes and proper motions of about half of 
the first magnitude stars, finds their average distance repre- 
sented by 40 light-years or 230 trillions of miles, a result con- 
firmed by D r Elkin's careful researches. — D. P. T. 



280 



Stars and Telescopes 



components, as suggested several years before by 
Michell in the Philosophical Transactions for 1767. 
Herschel, in 1782, began the practice of carefully 
observing and recording the relative positions and 




KNOWN DISTANCES OF STARS FROM THE SUN IN LIGHT-YEARS 

{From Todd's ' New Astronomy^ by special permission of the American 
Book Company, publishers) 



distances of the stars which he had noticed as being 
apparently closely double ; and when, after an inter- 
val of some years, these values were determined again, 
he at once discovered that in many cases the compo- 



The Fixed Stars 281 

nents of a double star have a distinct motion with ref- 
erence to each other. 

In Herschel's first paper on the subject, contained 
in the Philosophical Transactions for 1803, he remarks 
that his observations distributed over a period of twenty- 
five years, and there recounted, prove that many of 
the stars whose mutual positions and distances had 
been measured by him, 'are not merely double in 
appearance, but must be allowed to be real binary 

Orionis y Leonis Polaris y Virginis 




5 Cygni y A rietis y A ndromedcB 6 Serpentis 

EIGHT TYPICAL DOUBLE STAR SYSTEMS 

{As seen in an inverting telescope) 

combinations of two stars, intimately held together by 
the bond of mutual attraction/ These, then, are called 
binary stars, to distinguish them from such as are only 
optically double ; and the discoveries of binary sys- 
tems, or stars physically double, is constantly increas- 
ing. The high interest attaching to this subject has 
led many skilful astronomers to devote much attention 
to it since Herschel's time. The elder Struve was 
one of the first : and a catalogue of no fewer than 



282 



Stars and Telescopes 




F. G. W. STRUVE (1793-1864) 



3,134 double stars was published at Saint Petersburg 
in 1837, containing the results of his observations at 
Dorpat and Pulkowa. Many of the binary stars have 

a regular orbital revolution, 
the most interesting cases 
being £ Herculis, £ Ursae 
Majoris, and 70 Ophiuchi, 
whose periods of revolution 
have been determinedquite 
accurately to be 34, 61, and 
94 years respectively. The 
shortest known, those of k 
Pegasi and 8 Equulei, are 
only about eleven and a 
half years. Much longer 
than any of these, and therefore less precise, are the 
periods of those interesting and long-known double 
stars, y Virginis, y Leonis, and Castor, the first of 
which amounts to nearly 200, the second to about 
400, and the third to nearly 1,000 years. 

Accurate investigation of the proper motions of the 
larger stars has disclosed, by means of irregularities 
in these motions, more than one instance of the dis- 
turbance of a star by an unseen companion ; so that 
the binary character of the star was only discovered 
in this way. Such was the case with the brightest of 
all the fixed stars, Sirius ; and the disturbing compan- 
ion was afterward detected as a small star near it, 
visible only with a powerful telescope. Procyon, the 
principal star in Canis Minor, is also subject to a simi- 
lar irregularity of proper motion, and one which would 
seem to result from orbital motion round a companion 
possessing so feeble a luminosity that it was long sup- 
posed to be opaque ; and its probable perception has 



The Fixed Stars 



283 



been quite recent. The period of revolution in this 
case is about 40 years. 56 




W. R. DAWES (1799-1868) 



56 More than 10,000 double stars are now known, measured, 
and catalogued, a number only reached by the faithful enthu- 
siasm of many gifted astronomers — chief among them the 
Struves, father and son, 
Dawes, Professor Schiapa- 
relli, Baron Uembowski, 
and Professor Burn ham. 
Few stellar objects will better 
repay the amateur than ' dou- 
bles/ Even a small tele- 
scope will show many of 
the wider and brighter pairs, 
a few of which, illustrated on 
page 281, are readily located 
by ordinary star charts. The 
easiest is perhaps 7 Virginis, 
discovered by Bradley in 
1718; and it has now been 
measured through so large a 
portion of its binary arc that 

its period is pretty well established. The diagram on the next 
page exhibits the orbit and the observations upon which it is 
based. The real orbit has a high eccentricity, surpassing that of 
every other known binary. Of yet greater interest is Sirius, the 
orbit of whose companion, a star of the tenth magnitude, is 
also shown. The existence of this companion was first pre- 
dicted by D r Auwers, and verified independently in 1862 by 
Alvan Graham Clark, the distinguished optician, on the 
completion of the 18^-inch telescope now belonging to the 
Dearborn Observatory at Evanston. The accompanying dia- 
gram of the companion's orbit is by Professor Burnham, from 
observations between 1862 and 1896. There were no observa- 
tions between 1890 and 1896, because the companion was then 
so near the blazing central star as to be lost in its rays, and 
wholly invisible even with the Lick 36-inch telescope. It is 
now visible again, and will remain so till 1942, when it will 
disappear once more. The full period of the companion of 
Sirius is 51.8 years and its mass equals that of the Sun itself. 
The nearest known fixed star, a Centauri, is also a binary 



284 



Stars and Telescopes 



When stellar positions observed at considerable 
intervals of time are compared, nearly all the stars 

system with a period of 81 years (page 250). The component 
stars, very nearly equal, have each about the mass of the Sun. 
When at their nearest (periastron) they are about as far apart 
as Saturn is from the Sun, and at their farthest {apastron) their 
distance from each other is equal to 36 astronomical units, or 
one fifth greater than Neptune's distance from the Sun. About 
200 binary systems are now known, of which D r See regards 
40 as well ascertained. The longest known binary is f 




APPARENT ORBIT OF y VTRGINIS (2 1670) 

( The length of the major axis is nearly 7") 



apparent orbit of the 

companion of sirius 

(Burnham) 



Aquarii, with a period not less than 1,500 years; and among 
the very short ones not already mentioned are 82 Ceti (16 
years), and j8 883 (Lalande 9091), the shortest of all, with a 
period of 5-J years. 

A great gap still exists between even these short periods, and 
the times of revolution of companion stars recently discovered by 
means of the spectroscope, and therefore called spectroscopic 
binaries ; for their periods are not reckoned in years, but in 



The Fixed Stars 



285 



are found to be endowed with regular though slow 
changes of place in the heavens, called their proper 

days, or even hours. If the orbit of a close binary is seen 
■edge on, twice in every revolution the light of the two stars 
will coalesce ; half way between which the two stars will be 
moving, one toward and the other from the Earth, also twice. 
Now photograph the star's spectrum at each of these four 




ALVAN GRAHAM CLARK (1832-1897) 

critical points : in the first pair, the lines appear sharply 
single; in the second pair, they are found to be double. This 
singular phenomenon is readily explained by Doppler's im- 
portant and most useful principle (page 56), according to 
which the lines in the spectrum of a star receding from us are 
displaced toward the red, while if the star is coming toward 
us, the spectral lines are displaced toward the violet. At con- 



286 



Stars and Telescopes 



motions. Presently we shall consider whether these 
are in all cases wholly due to actual motion of the 



junction, then, as the two stars are passing athwart each other 
the lines in their combined spectrum will be single, but double 
at the quadratures, or intermediate between the conjunctions. 
Mizar (£Ursae Majoris) was the first discovered spectroscopic 
binary, by Professor Edward C. Pickering in 1889. This 
moderately bright star in the middle of the Dipper's handle 
has a mass exceeding that of the Sun forty-fold, and the period 




JOHANN CHRISTIAN DOPPLER (1803-1853) 

of its invisible companion is 52 days. £ Aurigas is another, 
with a much smaller mass and a period of four days. Also, 
a 1 Geminorum, the larger of the two stars composing the bril- 
liant double star Castor, proves to be a rapid binary with a period 
of only three days. But the case of yu 1 Scorpii is the most 
remarkable of all, with the exceedingly short period of 34 11 42™ 
30 s . On the same photographic plate, side by side, are the 
spectra of (x 1 and its companion yu 2 , the lines of the latter 



The Fixed Stars 287 

stars in space; but certainly a considerable part of 
the proper motions which are exceptionally large 
must be so. It has already been mentioned that 61 
Cygni was thought to be probably nearer us than most 
of the fixed stars, on account of its very large proper 
motion of about 5" in a year. Two small stars, one 
in the northern, the other in the southern hemisphere, 
having no designation but numbers in star catalogues 
(1,830 Groombridge, and 9,352 Lacaille), have 
proper motions even larger than this, being each 7" in 
amount, or nearly so \ but these stars do not, like 6 1 
Cygni, appear to be much nearer the solar system than 
others. Only a few stars are known to have proper 
motions between 4" and 5" in amount, and the proper 
motions of the great mass of stars are much smaller, 
and only to be recognized by comparing accurate 
observations widely separate in time. 

When the proper motions of several stars had been 
tolerably well determined, the idea was soon suggested 
that they might be due in part, not to actual motions 
of these stars in space, but to translation of the solar 
system among them. Such movement would produce 
an apparent motion in the stars in the opposite direc- 
tion to that of the solar motion, or a tendency on the 
whole to recede radially from the point in the heavens 

always single and sharply defined. Those of fi\ on the other 
hand, are now single and again double, thus leaving no room 
for doubting this most modern contribution of the spectroscope 
to stellar astronomy, and marvellously confirming the brilliant 
Bessel's prophecy of ■ the astronomy of the invisible/ By 
repeating these spectrum photographs and making compara- 
tive measurements upon them, the period of revolution and 
-other data can be found for binary stars so close together as 
to be forever beyond the separating power of the largest 
telescopes. — D. P. T. 



288 



Stars and Telescopes 



toward which the Sun was journeying. Approximate 
determinations of this point were simultaneously made 
in 1783 by Sir William Herschel and by Pierre. 
Prevost, of Geneva, both coming to the conclusion 
that it was situate in the constellation Hercules. In 
1805 Herschel made a similar investigation, founded 




STAR SPECTROSCOPE BY BRASHEAR 

{Attached to eye end of the 2,6-inch Lick telescope. Also shows accessory- 
apparatus for producing comparison spectra) 



on proper motions determined by Maskelyne; and 
in later times others were made by different astrono- 
mers, all of whom agree in placing the apex of the 
Sun's motion in the same region of the heavens, either 



The Fixed Stars 



289 



in Lyra or in the adjacent constellation Cygnus, and 
therefore not far from Hercules. 57 



57 Stellar proper motions were first made out by Halley in 
1718. M. Bossert, of the Paris Observatory, in 1896 published 
a catalogue of all the well-ascertained proper motions of stars, 
over 2,600 in number, in which the motion exceeds o 3 .oi in 
right ascension and o /7 .i in declination. An orange yellow 
star of the eighth magnitude in Pictor has a proper motion of 
nearly 9", the largest known. Sir William Huggins was the 
first to make, in 1868, that most important application of the 
spectroscope to sidereal astronomy, by which a star's light 
reveals unerringly its motion toward the Earth or from it, in 
accordance with Doppler's principle. Thus was demonstrated 
beyond a shadow of doubt the fact that the swarms of the 
stellar universe are in constant motion through space, not only 
athwart the line of vision as their proper motions had long dis- 
closed, but some swiftly toward our solar system and others 
as swiftly from it. So the term 'fixed stars' appeared to be 
a double misnomer. Research of this character has also been 
vigorously prosecuted by D r Vogel of Potsdam, near Berlin 
(page 61), at the Lick Observatory by Professor Campbell 
with the fine spectroscope shown above, and by M r Maunder 
at Greenwich (page 39), where the high significance of this 
work led the Astronomer Royal many years ago to direct its 
inclusion in the programme of observational routine. Follow- 
ing are a few determinations of 

Motion in the Line of Sight 











Motion per Second 


Star's Name 


Position for 


1900.0 




Toward or from the Sun 


Right Ascension 


Declination 


In Miles 


In Kilometers 


a Arietis 


h m 
2 2 



+22 


SQ 


-11. 7 


-19 


Aldebaran 


4 30 


+ 16 


18 


+31. 1 


+50 


Rigel 


5 10 


- 8 


iq 


+13.6 


+22 


Betelgeux 


5 50 


+ 7 


23 


+176 


+28 


y Leon is 


10 14 


-f20 


21 


-25.1 


-40 


Spica 


13 20 


— 10 


3« 


—106 


-17 


aCoronae 


15 30 


+27 


3 


+20.3 


+33 


Altair 


19 46 


+ 8 


36 


-23-9 


-38 



S & T — 19 



290 



Stars and Telescopes 



Attempts have been made to extend the theory far- 
ther, and to ascertain the region round which the 

The sign minus means that the star is coming toward us, 
and -f that it is receding. It is to be remembered that these 
are simply motions in the line of sight, relative to the solar 
system as a whole, for the effect of the Earth's motion round 




OBSERVATORY OF D r ISAAC ROBERTS, F. R. S. 
(Starfield, Crowborough Hill, Sussex, England) 

the Sun has been eliminated. To find the actual motions of 
these stars through space, it is necessary to combine the above 
data with their distances and proper motions, a geometric 
operation which will usually increase the sight-line motions 
very considerably. Part of the research regularly pursued 
with the 40-inch Yerkes telescope (page 338) is work of this 



The Fixed Stars 291 

solar motion is carrying the Earth and all the bodies 
that move obediently to the Sun. Such attempts,, 
however, are yet premature, and can only be regarded 
as tentative. Madler, about sixty years ago, consid- 
ered it probable that the point in the heavens in ques- 
tion was situate in or near the cluster of stars (see 
next paragraph) known as the Pleiades. But it would 
seem that the stellar motions noticed by him were 
rather due to special cases of star-drift ; and M r Max- 
well Hall, as the result of an investigation founded 
on the proper motions of a few stars whose parallax 
and distance are approximately known, has indicated 
a point in the constellation Pisces as that around which 
the solar motion is probably performed. In the pres- 
ent state of our knowledge, the period of this great 
revolution can be little more than matter of conjec- 
ture ; and as a rough approximation, it is put down 
by M r Hall at about 13,000,000 years. 

Many of the fixed stars are arranged in groups or 
constellations which imagination has likened to the 
forms of animals and other objects, — - some of these 
in strings of various twists suggesting the idea of ser- 
pents or dragons. While these groups are spread out 
over regions of the sky many degrees in extent, casual 
inspection of the heavens shows here and there a 
group of stars arranged close (sometimes very close) 
to each other, so as to form a cluster. Of these, the 
most remarkable is a loose cluster called the Pleiades > 

character, in charge of Professor Frost ; and photography is a 
most helpful adjunct, because the plates accumulated in periods 
of clear and steady atmosphere may thereafter be measured, and 
the necessary results derived at leisure and with that high degree 
of patience and painstaking which alone render such investiga- 
tions of any value. — D. P. T. 



2g2 



Stars and Telescopes 



in Taurus (pages 236-237). It is easy to perceive 
six stars in this well-known group, and some persons 
with unusually acute vision can detect several more ; 
but while Hyginus and Ovid say there are only six, 
there is evidence that as many as thirteen were seen 
before the invention of the telescope. With a moder- 







20-INCH REFLECTOR AND PARALLEL GUIDING TELESCOPE 
{Used by Dr Isaac Roberts in photographing stars and nebula) 

ately good instrument at least a hundred become visi- 
ble, while very large telescopes reveal the existence of 
more than a thousand. Near the Pleiades and in the > 
same constellation is a more scattered group called 
the Hyades, resembling a letter V. Still another, 
called Praesepe, is visible to the naked eye as a faintly 



The Fixed Stars 



293 



luminous spot or nebula in the constellation Cancer, 
and is not well seen unless the night be clear and 
moonless. The telescope, while showing that this and 
many other nebulous or cloudy-looking masses are 
composed of very distant or very minute stars, brings 
into view multitudes more not visible to the naked 




GLOBULAR CLUSTER IN PEGASUS 

{Photographed by Roberts, 4th November 1890. Exposure, 2 
hours. Central portion nebulous) 



eye at all. The close clusters are excellently illus- 
trated by the reproduction above, from photographs 
by D r Isaac Roberts, of a typical globular cluster in 
Pegasus, and the magnificent double cluster in Perseus 
(page 297) ; and on pages 290 and 292 are D r Rob- 



294 



Stars and Telescopes 



erts's observatory, and the ingenious arrangement of tel- 
escopes with which he took these classic photographs. 58 

58 And this is practically all that even the most powerful! 
telescope, if unaided, can avail. With it can be found the 
star's exact position in the firmament, not only with reference 
to neighboring stars, but its distance from us also. The 
telescope solved the problem of where, but was utterly baffled 
by the question what, until supplemented by the spectroscope, 
with observations interpreted by Kirchhoff's laws (page 69). 



1 I JL1 I |1 J ,1 L 



441.5 



438.4 



432.6 430, 




427.2 426.1 



SPECTRUM OF SIRIUS COMPARED WITH THAT OF IRON (VOGEL) 

Here again Sir William Huggins was the pioneer, and 
Betelgeux and Aldebaran were the first stars whose chemical 
constitution was revealed to the eye of man. Many of these 

distant twinkling luminaries 
were at once found to contain 
calcium, hydrogen, iron, mag- 
nesium, sodium and other met- 
als whose existence in the Sun 
had been demonstrated. What, 
for example, could be better 
proof of the fact of iron in Sirius 
than a spectrum like the one 
adjacent, in which are repeated 
coincidences of the dark (nega- 
tive) iron bands (above and 
below) with the intermediate 
bright lines of the spectrum 
of the star itself? Only a year 
intervened before the spectra 
of stars had been examined in 
pietro angelo secchi (1818-1878) numbers sufficient to permit 

their classification. This was 
first satisfactorily done by Father Secchi of Rome, whose 
comprehensive scheme embraced four distinct types based on 
optical observations solely : — 




The Fixed Stars 295 

Stretching across the sky in clear nights is seen a 
band or zone of luminous matter, which was a great 

Type I is chiefly characterized by the breadth and intensity 
of dark hydrogen lines ; also a decided faintness or entire lack 
of metallic lines (see next page). Stars of this type are very 
abundant, and are blue or white. Sirius, Vega, Altair and 
numerous other bright stars belong to this type, often called 
1 Sirian stars/ a class embracing perhaps more than half of all 
the stars. 

Type II is characterized by a multitude of fine dark, metallic 
lines, closely resembling the solar spectrum. They are yellow- 
ish, like the Sun. Capella (page 301) and Arcturus illustrate 
this type, often called ' solar stars/ and they are rather less 
numerous than the Sirians. According to recent results of 
Professor Kapteyn, absolute luminous power of first type stars 
■exceeds that of second type stars sevenfold. Stars nearest to 
the solar system are mostly of the second type. 

Type III is characterized by many dark bands, well defined 
on the side toward the blue, and shading off toward the red — 
a ■ colonnaded spectrum/ as Miss Clerke very aptly terms it 
(see the next page). Orange and reddish stars and a majority 
of the variables fall into this category, of which a Herculis, 
Antares and Mira are examples. 

Type IV is characterized by dark bands, often technically 
called flutings, similar to those of the previous type, but 
reversed as to shading : they are well defined on the side 
toward the red, and fade out toward the blue. Stars of this 
type are few, perhaps 50 in number, faint, and nearly all blood- 
red in tint. Their atmospheres contain carbon. 

Type V has been added to Secchi's classification by Pro- 
fessor Pickerxng, and is characterized by bright lines. They 
are about 70 in number, and are all found near the middle of 
the Galaxy. From two French astronomers who first investi- 
gated objects of this class, they are usually known as Wolf- 
Rayet stars. They are a type of objects quite apart from the 
rest of the stellar universe, and many objects termed planetary 
nebulae yield a like spectrum. 

A classification by D r Vogel combines Secchi's types III 
and IV into a single type, and several other classifications 
have been proposed since the inauguration of stellar spectrum 
photography. The Harvard classification embodies about 20 




H 
U 

W 

ex. 

"J 

W 

H 
O 

C/3 
W 

Ph 
>< 

H 

O ■ 

to 



a 

u 
u 

w 

ui 
W 

a 
< 



***. 

t 



The Fixed Stars 297 

enigma to the ancients, and received the name of the 
Galaxy, or Milky Way. As soon as Galileo applied 

groups. Whether these differences of spectra are due to. 
different stages of stellar development, or whether they indi- 
cate real differences of constitution, is not yet known. Prob- 
ably they are due to a combination of these causes. According 
to M r Espin, stars having the most bands in their spectra, 
present the greatest differences between their visual and photo- 
graphic magnitude. As in the Sun, so in the stars, the girdling 
atmosphere must be held responsible for numerous dark lines. 




DOUBLE CLUSTER IN THE SWORD HILT OF PERSEUS 

{Photographed by Roberts, 13th January 1890. Expostire, 3 hours. This cluster" 
is visible to the naked eye as a faint sj>ot of light in the Milky Way) 

In the case of a Aquilae, M. Deslandres, the able spectro- 
scopist of Paris, has discovered fine double bright lines 
traversing the middle of the dark hydrogen lines, also through 
the iron lines and the ^"-line of calcium ; and he traces their 
origin to a chromosphere similar to that enveloping our Sun. 

The first star whose spectrum was successfully photographed 
is Vega, by Henry Draper in 1872, and our detailed knowl- 
edge of stellar spectra is in great part consequent upon his 
initiative. At the time of his lamented death, research upon 
the constitution of the stars was still in the experimental stage ; 
but the ample funds of the Henry Draper Memorial, generously 



298 Stars and Telescopes 

his telescope to the heavens, he saw that this appear- 
ance is produced by millions of stars apparently scat- 
maintained by M rs Draper, have enabled Professor Pickering 
and his efficient corps to prosecute an unparalleled line of in- 
vestigations embracing the stars of both hemispheres. These 
researches were at first conducted with the Bache telescope, 
illustrated opposite, whose chief peculiarities are a large object 
glass of short focal length, and a mounting with a forked polar 




HENRY DRAPER (1837-1882) 

axis. For the furtherance of this work M rs Draper provided 
an exact duplicate of this instrument. Also, both are equipped 
with great prisms (not shown), mounted in front of the objec- 
tives, thereby spreading out the stellar images into lines on the 
photographic plate, instead of the mere points that appear on 
chart plates. Suitable adjustment of the prism and the clock- 
motion causes the broken spectral line to trail over the plate 
latitudinally, so that every star down to the eighth magnitude 



The Fixed Stars 



299 



tered like dust along the black ground of the sky. 
Analogy led many to suppose that the nebulae or 



records its own spectrum, sometimes many hundred on a single 
plate. The advantages of this fortunate arrangement are 
■obvious : peculiarities of spectra are continually leading to the 
detection of variable stars that would otherwise pass unob- 
served ; several new or temporary stars have been discovered ; 
and the spectra of about 50 stars in the Pleiades exhibit at a 
glance their close identity of chemical constitution. In 1890 




THE BACHE TELESCOPE AT CAMBRIDGE 
(Aperture, 8 inches. Employed since 1885 in photographing 
the stars and their spectra. Now mounted at A requipa, 
Peru, and in use upon the southern stars. The success 
of this photographic instrument led to the construction 0/ 
the Bruce telescope, page 264) 




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The Fixed Stars 



301 



smaller patches of lumi- 
nous matter brought into 

was published the ' Draper 
Catalogue of Stellar Spectra/ 
including more than 10,000 
stars ; and the larger and 
more powerful Bruce tele- 
scope (page 264) is now con- 
tinuing these researches to 
stars of fainter magnitudes. 
If a star's spectrum is re- 
quired with a high degree of 
dispersion, the ordinary slit 
spectroscope is employed, 
which so reduces the star's 
light that large objectives be- 
come necessary. D r Vogel 
and D r Scheiner at Pots- 
dam, and Sir Norman 
Lockyer at South Kensing- 
ton have likewise been suc- 
cessful in detailed photo- 
graphy of especially bright 
stars, recording many thou- 
sand lines in highly luminous 
objects of type II. Capella's 
spectrum adjacent, from a 
fine photograph kindly sent 
me by M. Deslandres of 
Paris, exhibits not only the 
wealth of lines, many of which 
are due to iron, calcium, he- 
lium and magnesium, but by 
displacement of bright lines 
in the terrestrial spectrum, 
shows the swift recession of 
Capella from our solar sys- 
tem. The door is now wide 
opened to a study of the 
constitution of at least the 
brighter stars in every detail 
of their chemical composi- 
tion ; and advance along these 



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302 



Stars and Telescopes 



view by telescopes are also masses of stars, resembling, 
on account of their greater distances, portions of the 
Milky Way as seen by the naked eye, — and, indeed, 
many of these were resolved into stars by more power- 
ful telescopes ; but (as just stated with regard to the 
great nebula in Orion) it is now known, from modern 




SIR JOHN F. W. HERSCHEL (1792-1871) 

observations with the spectroscope, that many of the 
nebulae are wholly or in part irresolvable. The improb- 
ability of the older view had been shown by Sir John 
Herschel's observations of those remarkable celestial 
objects in the southern hemisphere which, from hav- 
ing been first noticed by Magelhaens in the earliest 

lines cannot much longer be checked by the seemingly endless 
magnitude of the task. — D. P. T. 



The Fixed Stars 303 

voyage ever made to the Pacific Ocean, are called the 
Magellanic clouds. These consist of two large and 
nearly circular masses of nebulous light, — one larger 
than the other, — which are conspicuous to the naked 
eye, and look not unlike portions of the Milky Way. 
The larger remains visible even in strong moonlight, 
which obliterates the smaller. When viewed through 
large telescopes these objects are seen to contain mul- 
titudes of stars, and hundreds of nebulae which cannot 
be resolved into stars, all wedged together in such a 
way as to suggest some close and immediate connec- 
tion between them, quite inconsistent with the idea 
that any portions are at very much greater distances 
from us than others. 59 

59 Sir William Herschel, the goal of whose researches 
was a knowledge of the construction of the heavens, undaunt- 
edly essayed a tedious series of ' gauges ' or counts of the stars 
visible in different parts of the sky in the field of his 20-foot 
reflector. Twice the breadth of the field reached across the 
Moon's diameter; and the field itself contained about s^ooo" 
part of the area of the whole celestial sphere. Herschel 
actually counted the stars in nearly 3,500 such fields, and the 
number therein ranged all the way from o to nearly 600. These 
gauges were distributed all around the sky, along a galactic 
meridian inclined about 35 to the celestial equator, Sir John 
Herschel continuing his father's work at the Cape of Good 
Hope. The average number of stars in a field was as 
follows : — 

In the Galaxy itself 122 

In galactic latitude 15 30J 

30° I7f 

45° ioj- 

6o° 61 

75° 4* 

90 A\ 

From this very rapid increase in the number of the stellar 
hosts, as we approach nearer and nearer the Milky Way, 
Herschel drew unwarrantable conclusions, which we cannot 



304 



Stars and Telescopes 



The labors of the two Herschels greatly increased 
the number of known nebulae, and many more have 



-V- : ; ". 



■-'V 



THE NEBULAE AND CLUSTERS OF THE NORTHERN HEAVENS (WATERS) 

{Milky Way according to Boeddicker, the dots in it marking star dusters. The dots 
above a7id below it indicate nebulae, -most numerous in regions remote from the Galaxy") 



here enter into ; but we may summarize as follows our knowl- 
edge of this recondite subject down to the year 1890 : — 

The component bodies of our sidereal universe are scattered, 
without regard to uniformity, throughout a vast system having 
in general the shape of a watch, whose thickness is, perhaps, 



The Fixed Stars 



305 



been discovered since their time. About 10,000 are 
now catalogued, and their distribution over the celes- 



one-tenth of its diameter. On either side of this, and clustered 
about the poles of the sidereal system, are the regions of 
nebulae, thus making the entire visible universe spheroidal in 
general shape. The plane of the Milky Way passes through 
the middle of this stellar aggregation, and near its centre are 
our Sun and his attendant worlds. In large part, the stars are 
clustered irregularly, in various and sometimes fantastic forms, 
but without any approach to sys- 
tematic order. Often there are 
streams of stars ; and elsewhere 
aggregations leaf-like or tree-like 
in apparent structure ; also/ star- 
sprays,' as Proctor termed 
them. This painstaking investi- 
gator laboriously charted all the 
stars of Argelander's Durch- 
musteruiig, nearly 325,000 in 
number, and bare inspection of 
his comprehensive map affords 
the best notion of the seeming 
capriciousness of stellar distri- 
bution. But he proved clearly 
the detailed connection between 
the distribution of the stars and 

the complex branching and denser portions of the Galaxy. Sir 
John Herschel remarked many well-defined offshoots from 
the Milky Way, each tipped at its extremity with a fairly bright 
star; and the physical connection between the two may be 
regarded as certain. That is, the fainter stars of the Galaxy 
that give the effect of nebulous light are at practically the 
same distance as the brighter stars. Proctor, too, directed 
attention to the fact that the luminous streamers in the irregu- 
lar nebulae often coincide with streams of small stars in the 
same field ; and in the case of Orion, spectroscopic analysis by 
Sir William and Lady Huggins has proved the connection 
between wisps of the nebulous light and the stars adjacent, 
thus leaving little room for doubt as to the distance of the 
nebulae. See also the nebulous streamers of the Pleiades 
(page 237). Upon such inference, in fact, our slender knowl- 




r. A. proctor (1837 



306 Stars and Telescopes 

tial vault — by no means uniform — manifests a marked 
tendency to avoid the zone of the Milky Way, and to 

edge of the distance of the nebulae depends; for the parallax 
of a nebula, although attempted, has never been measured 
directly. 

Since 1890 the spectroscope has come to the assistance of 
the telescope in solving the intricate problem of stellar distri- 
bution. Professor Pickering had noticed that most of the 
brighter stars of the Galaxy yield spectra of the first or Sirian 
type ; and Professor Kapteyn, by combining the well -ascer- 
tained proper motions of certain stars with their classification in 
the ' Draper catalogue of stellar spectra,' concludes that, as stars 
having very small proper motions show a condensation toward 
the Galaxy, the stars composing this girdle are in great part of 
the Sirian type and lie at vast distances from the solar system. 
If a star is near to us, its proper motion will ordinarily be large ; 
and in the case of stars of the second or solar type, the larger 
the proper motion the greater their number. So it would ap- 
pear that the solar stars are aggregated round the Sun himself; 
a conclusion greatly strengthened by the fact that of stars 
whose distance and spectral type are both ascertained, seven 
of the eight nearest to us are solar stars. 

From Professor Kapteyn's further research he concludes 
that our solar system lies, not at the centre, but slightly to the 
north of the Galaxy. Returning then to the Sirian stars, he 
reaches the conclusion that if we compare stars of equal bright- 
ness, those of the Sirian type average nearly three times more 
distant from the Sun than do those of the solar type. The 
Sirian stars may therefore be legitimately regarded as far ex- 
ceeding the solar stars in intrinsic brightness. Gould's theory 
of a solar cluster receives remarkable confirmation, though the 
evidence as to the figure of this cluster is far from complete ; 
indeed, it may be ring-shaped. But Professor Kapteyn's con- 
clusion seems hard to escape, that the Galaxy itself has no 
connection with our solar system ; and is composed of a vast 
encircling annulus of stars, far exceeding in number those of 
the solar aggregation, and everywhere more remote than the 
stars composing it, as well as differing from them in physical 
type. So it is the mere element of distance that reduces their 
individual glow and seemingly crowds them thickly together 
into that gauzy girdle which we call the Galaxy. — D. P. T. 



The Fixed Stars 307 

aggregate north and south of it, near the poles of the 
galactic circle, as illustrated on page 304. This is addi- 
tional proof that the nebulae are connected with the 
general system of the stars, and do not form other 
systems, as was formerly thought, at immense dis- 
tances beyond it. Sir John Herschel noticed that 
one third of the nebulae catalogued by him, chiefly 
from his father's and his own observations, are con- 
gregated in a portion of the heavens occupying about 
one eighth of the celestial sphere, extending from 
Ursa Major in the north to Virgo in the south. If the 
irresolvable nebulae are not placed at distances from us 
immensely greater than are those that have been re- 
solved into clusters of stars, what is the alternative? 
Simply that the irresolvability of the former arises, not 
from the greater distance of the stars comprising 
them, but from their actually smaller size, which pre- 
vents their being seen separate, even under the high- 
est telescopic power. 

We conclude with a few words respecting three of 
the most interesting of the nebulae. The most re- 
markable of all surrounds Orionis and is in that part 
of the constellation Orion called ' the sword.' Only 
barely visible to the naked eye, it appears to have 
been first seen by Cysat, a Swiss astronomer, in 16 18. 
It was first drawn and described by Huygexs (who 
was apparently unaware of Cysat's perception) thirty- 
seven years afterward. Although this gigantic object 
contains a large number of telescopic stars, spectral 
analysis has shown that a portion of the light received 
from it, and from some other nebulae as well, is due 
to glowing gas (page 238). 

The great nebula in Andromeda (page 243) is just 
visible to the naked eye, and was noticed before the 



3o8 



Stars and Telescopes 



invention of the telescope, there being evidence that 
Al-Sufi, the Persian astronomer/ saw it in the tenth 
century of our era. Simon Mayr first examined it 
telescopically and described it in 1612. A very in- 
teresting nebula in the southern hemisphere and invisi- 
ble in our northern latitudes, surrounds the remarkable 
variable star 77 Argus. The first to describe this object 
seems to have been the French astronomer Lacaille, 
in the course of his observations, in 1750-53, at the 
Cape of Good Hope, when Sir John Herschel in the 
following century drew an elaborate representation of 
it, which still serves as a standard of comparison. 60 

60 Regarding the nebulae as the primordial substance that 
worlds are fashioned from, our ultimate knowledge of the con- 
struction of the heavens rests 
upon (1) the discovery and 
classification of thousands of 
nebulae, (2) the accurate deter- 
mination of their positions 
among the stars (repeated at 
long intervals), (3) the study of 
their physical appearance in 
the telescope and by means of 
photography, (4) their motions 
in space and chemical constitu- 
tion by the spectroscope, (5) 
determinations of their distance 
by the stars to which they are 
found to be related. About 
8,000 nebulae are now recorded 
in our catalogues, the most 
complete of which is that by 
D r Dreyer of the Armagh Ob- 
servatory in Ireland. The keen- 
eyed D r Swift, now work- 
ing in the clear skies of Southern California, is continually 
adding new discoveries. Following the Herschels came La- 
mont of Munich and D'Arrest of Copenhagen, who devoted 
many faithful years to observation of the nebulae. Large tele- 




lamont (1805-1879) 



The Fixed Stars 



309 




scopes are now requisite for continuing this important work, 
such as the 26-inch refractor of the University of Virginia, em- 
ployed to good advantage in this field by Professor Stone. 
The Orion nebula was the first one ever photographed, by 
Henry Draper in 1880, and nebular photography has been 
successfully followed up by D r von Gothard in Hungary ; 
by Professor Barnard who has discovered extensive masses 
of diffused nebulosity outside 
the Pleiades, and an optically 
invisible nebula of vast extent 
in Scorpius ; by Professor 
W. H. Pickering, whose 
plates reveal spiral filaments 
outlying the nebula of Orion ; 
and by Dr Isaac Roberts. 
whose fine photographs of 
star clusters, the Orion nebula 
(page 238) and the La Placian 
ring nebula in Andromeda 
(page 243) have already been 
shown. The spectrum of the 
latter shows that it is not 
gaseous, still no telescope has 
yet resolved it. Two other 
products of his remarkable 
skill and patience here follow 
— the ringnebulain Lyra (notagood reproduction of his original 
negative), and the marvellous spiral nebula in Canes Venatici, 
the characteristic whorls of which, as drawn by Lord Rosse, had 
been doubted by many astronomers till this photograph revealed 
them convincingly. Here we seem to see a multiple star in 
process of actual evolution, much as the double stars are 
thought to have originated from the double nebulae (page 251). 
Following in the footsteps of Sir John Herschel, D r Gill at 
the Cape, Mr Russell, Government Astronomer at Sydney, 
and Professor Bailey at Arequipa, have continued the highly 
important task of photographing the southern nebulae and 
clusters with eminent success. In 1897 Bailey photographed 
a fine spiral nebula in Hydra. Wide zones of the southern 
sky, however, remain yet unexplored, except the mere recon- 
naissance. Evidences of variability have been sought in dif- 
ferent regions of several of the larger nebulae ; but only a single 
instance of change is satisfactorily made out — in the great 



RING NEBULA IN LYRA 

[Photographed by Roberts, 17 tk 
yuly 1 89 1. Exposure 30 minutes. 
The central star, very obvious in 
the photograph, is an exceedingly 
difficult object, even with great 
telescopes) 



3io 



Stars and Telescopes 



irregular nebula enveloping 77 Argus (page 265), a conspicuous 
part of which, recorded near the centre of Herschel's draw- 
ing, is wholly absent from M r Russell's photograph of 1890,. 
in which the same space is occupied by a great dark oval. 
The facts of highest significance concerning nebulae recently 
brought to light depend upon observations with the spectroscope 

by Professor Keeler, now 
director of the Lick Obser- 
vatory. Sir William 
Huggins in 1864 fi rs t 
found bright lines in their 
spectra, evidencing a com- 
munity of chemical compo- 
sition, and due to glowing 
gas, mostly hydrogen. Re- 
cently helium has been 
added, and still other lines 
are due to substances as 
yet unrecognized on the 
Earth. The character of 
the lines indicates exceed- 
ingly high temperatures,, 
or a state of strong electric 
excitement. Temperature 
spiral nebula in canes venatici and pressure both increase 
{No. 51 in Messier's Catalogue. Photo- toward the nucleus. Not 
graphed by Roberts, 29M April 1889. all the nebulae yield bright 
Exposure, 4 hours. The most marked ] me s ; and this may be due 
of the spiral nebulae) ^ gag under extreme pres . 

sure, or to aggregations of 
stellar bodies. There are about forty lines in the photographic 
spectra of nebulae, the chief line, according to Professor 
Keeler, failing of identity with the magnesium fluting. His 
careful measurements upon the spectra of the Orion nebula 
are perhaps the most significant of all, for they prove that 
the distance between the nebula and our solar system is in- 
creasing at the rate of eleven miles in every second of time. 
However, neither this nor any other nebula has been discovered 
to partake of proper motion, although the bright nebula in 
Draco is coming toward us at the rate of forty miles per sec- 
ond. All the evidence so far seems to show that the nebulae 
are in motion through interstellar space with velocities com- 
parable with those of the stars themselves. — D. P. T. 




The Fixed Stars 311 

Struve, W., Slellarum Compos it arum Mensurae Micrometricae 

(Saint Petersburg, 1837). See also Dun Echt Observatory 

Publications, i. (Aberdeen, 1876). 
Struve, W., Etudes d'Astronomie Stellaire (Saint Petersburg, 

1847). 
Smyth, W. H., ' Colors of Multiple Stars' Sidereal Chromatics, 

(London, 1864). 
Huggixs, 'Motion in Sight-line,' Proceedings Royal Society 

xvi. (1866), 382. 
D' Arrest, Siderum Nebulosorum Observatio?ies Havnienses 

(Copenhagen, 1S67). 
Wolf, Rayet, ' Bright-line Stars/ Comp. Rend. lxv. (1867), 292. 
Huggins, ■ Resume of Spectrum Analysis,' Report British As- 
sociation, 1868, pp. 140-165. 
MONTIGNY, ' Scintillation,' Bulletins de V Academie de Bel- 

gique, 1868, et sea. 
Proctor, Universe and Coming Transits (London, 1874). 
Knobel, ' Bibliography of Stars and Nebula,' Month. Not. Roy, 

Astr. Soc. xxxvi. (1876), 365. 
NEWCOMB, Popular Astronomy (New York, 1877). 
Knobel, ' Chronology of Star Catalogues/ Mem. Roy. Astr, 

Soc.xlm. (1877), 1. 
Hall, M., ' Sidereal System/ Memoirs Royal Astronomical 

Society, xliii. (1877), 157. 
Hall, A., ' Double Stars/ Washington Obs. 1877, App. vi. 
Holdex, 'Nebula of Orion/ Washington Obs. 1878, App. i. 
Secchi, Les Etoiles (Paris, 1879). 
Crossley, Gledhill, Wilson, Handbook of Doicble Stars 

(London 1879), Notes, etc. (1880). Bibliographies. 
Rosse, ■ Observations of Nebulae and Clusters, 1848-78/ Trans. 

Roy. Soc. Dublin, ii. (1880). 
Pickerixg, ' Dimensions of Stars/ Proc. Am. Acad. Arts and 

Sciences, viii. (1881), 1. 
Plummer, 'Sidereal System/ Copernicus, ii. (1882), 45. 
Newcomb, 'Catalogue of Standard Stars/ Astr. Papers Am. 

Ephenieris, i. (1882), 147. 
Vogel, Muller, ' Stellar Spectroscopy/ Publ. Astrophys. Obs. 

Potsdam, iii. (1883). 
Plummer, ■ Sun's Motion in Space/ Mem. Roy. Astron. So- 
ciety, xlvii. (1883), 327. 
Graxt, 'Catalogue of 6415 Stars/ Glasgow Univ. Obs. (1883). 
Gill, Elkix, 'Parallaxes in So. Hemisphere/ Mem. Roy. Astr, 

Soc. xlviii. (1884), 1. 



312 Stars and Telescopes 

Yarnall, Frisby, 'Catalogue of 10,964 Stars/ Washington 

Observations, 1884, Appendix 1. 
Draper, ' Stellar Spectrum Photography/ Proc. Am. Acad. xi. 

(1884), 231. 
Gill, * Future Problems in Sidereal Astronomy/ Proc. Roy. 

Institution, xi. (1884), 91. 
Pritchard, Uranometria Nova Oxoniensis (Oxford, 1885). 
Pickering, c Harvard Photometry/ Annals Harv. Coll. Obs. 

xiv. (1885); xxiv. (1890). Bailey, xxxiv. (1895). 
Pickering, ' Photographic Photometry/ Ann. Harv. Coll. Obs. 

xviii. 1888, No. VII. 
Gore, J. E., Planetary and Stellar Studies (London, 1888), 
Lockyer, 'Classification/ Proc. Roy. Society, xliv . (1888), 1. 
Dreyer, ' Catalogue of Nebulae and Clusters/ Mem. Roy. Ast. 

Soc. xlix. (1888), 1 ; li. (1895), 185. 
Pickering, ' Index to Observations of Variables/ Annals 

Harvard College Observatory, xviii. (1889), No. vin. 
Chandler, ' General relations of variables/ The Astronomical 

Journal, ix. (1889), 1. 
Pritchard, Researches in Stellar Parallax by the Aid of 

Photography (Oxford, 1889-92). History, iv. (1892). 
Chambers, Descriptive Astrono?ny, iii. (Oxford, 1890). 
Clerke, The System of the Stars (New York,i89o). 
Boss, f Solar Motion/ The Astronomical Journal, ix. (1890), 161. 
Pickering, ' Draper Catalogue of Spectra/ Ann. Harv. Coll. 

Obs., xxvii. (1890) ; Maury, xxviii. (1897). 
Russell, Description of the Star Camera (Sydney 1891). 
Scheiner, ' Photographic Photometry/ Astronomische Nach- 

richten, cxxviii. (1891), 113. 
PIuggins, 'Celestial Spectroscopy/ Nature, xliv. (1891), 372. 
Rambaut, ' Binary Orbits by Spectroscope/ Month. Not. Roy. 

Astron. Society, li. (1891), 316. 
Boeddicker, The Milky Way (London and New York, 1892). 
Proctor, Ranyard, Old a7id New Astronomy (London, 1892). 
Vogel, Newcomb-Engelmann's Populare A stronomie (Leip- 
zig, 1892). 
Vogel, ' Motion in Sight-line/ Astronomy and Astrophysics, 

xi. (1892), 203. 
Porter, 'Proper Motions/ Publ. Cincinnati Obs. xii. (1892). 
Ball, The Story of the Heavens (London, 1893). 
Gore, J. E., * Sun's Motion in Space/ The Visible Universe, 

p. 193 (New York, 1893). 
Easton, La Voie Lactee (Paris, 1893 ). 



The Fixed Stars 313- 

Roberts, Photographs of Stars and Nebulcc (London, 1893). 
Belopolsky, '/SLyrae/ Mem. Spettroscopisti Ital. xxii. (1893). 
Clerke, History of Astronomy during the XlXth Century. 

(London, 1893). 
Lockyer, * Spectra of the brighter stars/ Phil, Trans, clxxxiv* 

(1893), 675. 

Ball, ' Solar Motion/ In the High Heavens (London 1893). 

Vogel, ■ j8 Lyrae/ Sitz. Akad. Wiss. Berlin 1894 (1), 115. 

Janssen, ' Photographic Photometry/ Smithsonian Report 1894,. 
p. 191. 

Scheiner, Frost, Astronomical Spectroscopy (Boston and Lon- 
don, 1894). Bibliography. 

Campbell, ' Wolf-Rayet Stars/ Astronomy and Astrophysics,. 
xiii. (1894), 448. 

Gore, J. E., The Worlds of Space (London, 1894). 

Muller, Kempf, * Photometry/ Publ. Obs. Potsdam, ix. (1894). 

Flammarion, Gore, Popular Astronomy (New York 1894). 

Madler, Burnham, ' Double Stars/ Himmel und Erde, vii. 
(1894), 41. 

Burnham, ' Double Stars/ Publ. Lick Observatory, ii. (1894). 

Keeler, 'Spectra of Nebulae/ Publ. Lick Obs. iii. (1894); 
Astron. and Astrophys. xiii. (1894), 476. 

Giberne, Radiant Suns (New York, 1894). 

Chambers, The Story of the Stars (New York, 1895). 

D'Engelhardt, ' Nebulae and Clusters/ Observations Astro* 
nomiques (Dresden, 1895). 

Samter, ' Milchstrasse/ Himmelund Erde, vii. (1895), 5°%> 544* 

Valentiner, Handworterbuch der Astron. (Breslau 1895-98). 

Chandler, ' Catalogue of Variables/ The Astronomical Jour- 
nal, xvi. (1896), 145. 

Radau, ■ Solar Motion/ Bulletin Astron. xiii. (1896), 169. 

Everett, ' Poles of Binary Orbits/ M. N. Roy. Astr. Soc. lvi. 
(1896), 462. 

See, Researches on the Evolution of Stellar Sy stems (Lynn, 1896). 

Ceraski. 'Variables/ Annates Obs. Moscou, iii. (1896), livr. ii. 

Chase, ' Cluster in Coma Berenices/ Trans. Yale Obs. i. (1896). 

Moulton, ' Spectroscopic Binaries/ Pop. Astr. iii. (1896), 337. 

Clarke, H. L., ' Life-history of Star Systems/ Pop. Astr. iii.. 
(1896), 489. 

Russell, ' Southern Circumpolars/ Pop. Astr. iv. (1896), 61. 

Burnham, ' Binary Systems/ Popular Astr. iv. (1896), 169. 

Gill, Kapteyn, ' Photographic Durchmusterung/ Annals 
Cape Observatory, iii. (1896); iv. (1897). 



3 14 Stars and Telescopes 

Yendell, 'Variable Stars/ Popular Astr. iii.-v. (1896-97). 
Schiaparelli, ' Color of Sirius/ Rubra Canicula (1897). 
Lockyer, ' Celestial Eddies,' Nature, lv. (1897), 249. 
Fowler, ' Chemistry of the Stars,' Knowledge, xx. (1897), yy. 
Monck, ' Spectra of Binaries/ The Observatory, xx. (1897), 389. 
Clerke, *)8 Lyrae/ The Observatory, xx. (1897), 410. 
Scheiner, Die Photographie der Gestime (Leipzig, 1897). 

Atlas and bibliography. 
Gould, 'Clusters/ Cordoba Photographs (Lynn, 1897). 
Whitney, ' Solar Motion/ Popular Astronoiny, v. (1897), 309. 
Wilson, 'Ring nebula in Lyra/ Popular Astr. v. (1897), 337. 
Clerke, ' New Class of Variables/ Observatory, xx. (1897), 52. 
Muller, Die Photometrie der Gestime (Leipzig, 1897). Biblio- 
graphy. 
Hall, M., ' Sidereal system revised/ M. N. Roy. Astr. Soc. lvii. 

(1897), 357 5 lviii. (1898), 473. 
Pannekoek, '/3 Lyrae,' Kon. Akad. Wetenschap. Amsterdam, 

v. (1897). 
Huggins, ' Celestial Spectroscopy/ The Nineteenth Ce?itury 9 

xli. (1897), 907. 
Lockyer, The Sun's Place i7i Naiure (London, 1897). 
Pannekoek, ' Galaxy/ Jour. Brit. Ast. Assoc, viii. (1897-98). 
Gore, J. E., ' Sidereal Heavens/ Concise Knowledge Library 

(New York, 1898). 
Duner, Scheiner, ' Stellar Evolution/ Popular Astr. vi. 

(1898), 85. 
Myers, ' System of /3 Lyras/ The Astrophysical Journal, vii. 

(1898), 1; Popular Astronomy, vi. (1898), 268. 
Keeler, ' Physiological Phenomena, and Spectra of Nebulae/ 

Publ. Astr on. Society Pacific, x. (1898), 141. 
Kapteyn, * Solar Motion/ Astron. Nachr. cxlvi. (1898), 97. 
Easton, i Theory of Universe (Proctor)/ Knowledge, xxi. 

(1898), 12. 
Easton, 'New Theory of Galaxy,' Knowledge, xxi. (1898), 57. 
Maunder, McClean, ' Photographs of Stellar Spectra/ Ob- 
servatory, xxi. (1898), 163. 
Schweiger-Lerchenfeld, Atlas der Himmelskunde (Vienna, 

1898). 
Deslandres, ' Motion in Sight-line/ Bulleti?i Soc. Astron. 

France, September 1898. 
McClean, * Stellar Spectroscopy/ Proc. Roy. Soc. lxiv. (1898). 
Douglass, ' Stellar Bands in Zodiac/ Pop. Astr. v. (1898), 511. 
Eastman, Catalogue of 5,151 Stars (Washington 1898). 



The Fixed Stars 



315 



Deslandres, 'Motion in Sight-line,' Bulletin Astrou. xv. 

(1S9S), 49. 
Young, General Astronomy, revised edition (Boston, 1898). 
Hagen, Atlas Stettarum Variabilium (Berlin, 1898). 

References to the popular literature of the stars and nebulae 
are to be found in the volumes of Poole's Index, on the 
pages indicated below : — 



Volume of Index, and Years 


References 
to Nebulas 


References 
to Stars 


I (1S00-81) 

II (1S82-86) 

III (1887-91) 

IV (1892-96) 

Annual Literary Index, 1S97 
Index to General Literature, 1893 


P-903 
308 
298 
396 
89 
203 


P-I243 

417 
407 

545 
122 

274 



Most of the earlier and more important scientific papers are 
classified and titled in Sir Robert Ball's Elements of Astron- 
omy, pp. 427-40 (New York, 1880). In vol. xxxii. (1883) of the 
Proceedings American Association Adz'anceme?it of Science, 
W. A. Rogers has given a full presentation of the German 
survey of the northern heavens. The occasional bulletins of 
the Paris astrographic conference contain important researches 
relating to stellar photography and allied subjects. Recent 
volumes of Knowledge contain numerous papers on the stars 
and nebulae, by M r Maunder and others, with fine reproduc- 
tions of astronomical photographs, especially those of D r 
ROBERTS. In the Journal of the British Astronomical Association 
are found very useful lists and abstracts of papers. Occasional 
bibliographic lists are given in Bulletin Astronomique, i.-xv. 
(1884-98). Recent scientific literature is exhaustively cited in 
the frequent lists of the Astrophysical Journal, vols, i.-viii. 
< 1895-98). —D.P. T. 



CHAPTER XVIII 

TELESCOPES AND HOUSES FOR THEM 

T^NOWLEDGE of the Sun, Moon and stars gained 
A *" from the preceding chapters leads naturally 
to a brief story of the instrument by which astrono- 
mers have mainly acquired that knowledge; for 
before the invention of the telescope, it was impos- 
sible that mankind should know very much about the 
heavenly bodies. The working of a telescope is- 
much affected by its location and the construction of 
the building in which it is sheltered : a few para- 
graphs are therefore devoted to these important 
considerations. 

Galileo (page 12), while not perhaps the original 
inventor of the telescope, was still undeniably the- 
first to construct one and apply it to the higher pur- 
pose of astronomical observation, and he was richly- 
rewarded by the supreme discovery of the satellites of 
Jupiter. Before his day, not only were no bodies 
attendant upon the planets known, save our Moon, 
but many of the planets were themselves unknown - r 
nor was it possible to ascertain the dimensions of 
those that were known. The accepted truth of the 
Copernican system had led to the prediction of phases- 
of the planets nearest the Earth and Sun ; but final 
corroboration was lacking till the first telescope 
achieved this significant revelation. Several cata- 



Telescopes and Houses for Them 3 1 7 



logues of the stars and Tvcho's observations of the 
planets among them were possible, before the days of 
telescopes \ but so crude were they that their value at 
the present time is due solely to their antiquity. 
Although invented early in the 17 th century, the 
telescope was chiefly used as a gazing instrument for a 
half century; 

and it was not till /|fl ""^N 

1668 that the 
mechanical ge- 
nius of Jean 
Picard (1620- 
1682) saw how 
greatly the tele- 
scope might en- 
hance the pre- 
cision of all 
astronomical 
measures of po 
sition, if only it 
were attached to 
a circle to impart 
definiteness of 
alignment. Al- 
though R OMER 
(page 45) had invented the transit instrument, Pic- 
ard's invention produced the meridian circle, a mod- 
ern type of which is shown on page 368 ; with it may 
be found the exact place of any heavenly body on 
the celestial vault with the utmost ease and celerity. 
However, even the transit or the meridian circle 
would be greatly restricted in use but for the astro- 
nomical clock, the principles governing the pendulum 
of which had been formulated by Galileo. But here 




christian huygexs (1629-1695) 



3i8 



Stars and Telescopes 



was a delay of nearly a half century, for it was not till 
1657 that Huygens, famous for his great telescopes 
and the observations made with them (especially of 
the planet Saturn), constructed an accurate time-piece 
by controlling its train with a pendulum. 




TYPICAL GREAT TELESCOPE OF THE I7TH CENTURY 
{Built and used by Hevelius at Dantzig) 



In the telescopes of Galileo and Huygens and all 
their followers for about a century, the image of a 
remote object was formed by a single lens of double 
convexity. The glass was full of imperfections ; but 
besides this, the baffling obstacle of the prismatic 
spectrum surrounded all bright objects with highly 



Telescopes and Houses for Them 319 

colored fringes, so that a limit to the effective size of 
the telescope seemed to be set by the laws of nature 
herself. But it was soon found that the disturbing 
color effects were minimized, if the lens was ground 
very flat. This, however, necessitated great focal 
length, and many telescopes were built in the 17th 
century with but little variation in model from the 
famous instrument of Hevelius (1611-1687) illus- 
trated above; in which ob- 
ject-glass and eye-piece were f 
so far apart that no tube con- ttftl^ ' fT 
nected them, and they were jjjWfe f'gj 1 1 
kept in line by an open 1 W& ' I E; I 
framework, strongly trussed. JBI | SI II 
Huygens built an aerial tele- ^"gpr 
scope, with objective and eye- SB JHi 
piece wholly unconnected, ^^^ ^^* 
the former being mounted in A MODERN FIELD . GLASS 

a Small Swivel tube On top Of { B y Bausch & Lome. A ray of 

a high pole, and directed li z ht comin z do ™ n through the 

° 1 8 objective follows the arrow ^ is 

toward the eye-piece by a four times refected in prisms 

cord or wire pulled taut by the £££££*' ** « ih ° 

observer. Definition was ex- 
ceedingly imperfect except at the centre of the field 
of view, wind precluded the use of the telescope, and 
except for a moment at a time it was practically im- 
possible to maintain the object in the field with that 
steadiness requisite for critical observation. Never- 
theless, the long telescope had its day, and one 600 
feet in length is said to have been made in Italy, though 
never successfully used. 

Galileo's original telescope had but two lenses : a 
double convex to form an image, and a double con- 
cave to examine it with ; and this form of telescope 



320 Stars and Telescopes 

is preserved in the common opera-glass and field-glass 
of the present day, if only slight magnifying power is 
desired. Great improvement in optical power has, 
however, been recently obtained by adjusting two 
right-angled prisms, properly constructed, in the path 
of the rays between objective and eye-pieces, whereby 
the necessary compactness of a hand-glass is secured, 
and with it the advantages of greater focal length and 
a larger image at the focus. At the same time the 
prisms effect that reinversion which is requisite for 
terrestrial purposes. A magnification of 15 diameters 
and more is easy. 

Sir Isaac Newton (page 93), who was no less a 
physicist than astronomer, after devoting many years 
to a study of the imperfections of refracting tele- 
scopes, expressed a definitive opinion that a perfect 
glass of high power was a physical impossibility ; and 
this conclusion, coupled with the unwieldy propor- 
tions of the most powerful instruments of that day, 
forestalled farther attempts to improve the refractor 
or dioptric telescope. But the genius of Newton led 
the way by modifications of the reflector, or catoptric 
telescope, already invented by James Gregory (1638- 
1675), which forms the image of a distant object by 
convergence of the rays on reflection from a concave 
surface of suitable curvature and high polish. In the 
refractor, the object-glass assembles rays of different 
colors at different focal points, the violet nearest the 
glass and the red farthest from it ; but in the reflec- 
tor all rays are focussed at a single point, no matter 
what their color. Still, as the image is formed directly 
in front of the mirror itself, the head of the observer, 
if placed in the ordinary position, would intercept 
nearly all rays from the object. Gregory had dodged 



Telescopes and Houses for Them 321 

this difficulty by mounting a small secondary concave 
mirror in the path of the rays, thus throwing them 
back upon the primary mirror. This he perforated 
at the centre to allow the doubly reflected rays to 
reach the eye-piece, which was then screwed into the 




A MODERN REFLECTOR 

{Newtonian type by Bra shear. Eye-piece near 
the ,, fi7ider ' at upper end of tube) 



back of the large reflector. Newton improved upon 
this arrangement and preserved the principal mirror 
intact by interposing a small diagonal reflector in the 
path of the rays just before they come to a focus, 
thereby diverting them to the side of the tube, where 

S & T — 21 



322 



Stars and Telescopes 



the eye-piece is set perpendicular to it. The obser- 
ver then looks into the tube, not at one end, but at 
one side, at right angles to the direction of its point- 
ing. The Newtonian is the favorite type of construc- 
tion for the reflector at the present day, especially if 
moderate in size, as in the preceding illustration of a 

Newtonian by M r John 
A. Brashear of x\lle- 
gheny, who, of all Am- 
erican opticians, has 
achieved the greatest 
success in constructing 
reflectors. A farther 
improvement of the 
Newtonian form, by 
substituting a small to- 
tally reflecting prism 
for the secondary mir- 
ror, was carried into 
effect by Henry 
Draper. 

During the past cen- 
tury five builders of re- 
flecting telescopes have stood out pre-eminently : Sir 
William Herschel, whose 4-foot reflector is illustrated 
on page 13, and who long served a self- apprenticeship 
by constructing nearly 200 mirrors, one of them 24 
inches in diameter which was nearly equal in per- 
formance with the 4- foot, and with which his son, Sir 
John, continued the elder Herschel's researches ; 
Lord Rosse, whose ' Leviathan/ or 6-foot reflector 
illustrated on page 247, remains yet unsurpassed in 
size; William Lassell (1 799-1 880), an eminent 
English astronomer, who built two reflectors, dupli- 




4-FT. MELBOURNE REFLECTOR 
{Designed and built by Thomas Grubb) 



Telescopes mid Houses for Them 323 

cates in size of Herschel's largest instruments, which 
he used on the island of Malta, 1852-65 ; Thomas 
Grubb, who in 1867 built a 4-foot Gregorian with a 
silver-on-glass speculum for the government observa- 
tory at Melbourne, Australia, and who has a worthy- 
successor in his son, Sir Howard, the builder of the 




THOMAS GRUBB (180O-1878) 



20-inch reflector illustrated on page 292, with which 
D r Roberts has produced photographs of unusual ex- 
cellence ; and D r A. A. Common, of Ealing, England, 
whose first great reflector of 3-foot aperture is now 
owned by the Lick Observatory, by gift of M r 
Edward Crossley, and who built in 1889 a 5 -foot 
silver-on-glass reflector, employed to good advantage 
in photographing the nebulae. An instrument of like 



324 Stars and Telescopes 

dimensions is now building at the Yerkes Observatory 
of the University of Chicago. 

It will be noticed that all the great reflectors pre- 
viously mentioned were constructed in Great Britain, 
and that they achieved extraordinary Success in the 
hands of their builders. A great reflector is, indeed, a 
delicate instrument, requiring much skill and patience 
in adjusting, and more than ordinary care in preser- 
vation of the specular surfaces from deterioration on 
exposure to the atmosphere ; but by M r Brashear's 
formula, a new film of silver is readily deposited upon 
the glass chemically. Besides this, the great reflector 
is exceedingly massive, and unwieldy in proportion ; 
and its performance is much influenced by disturbing 
air-currents, while flexure or sagging of the mirror is 
a most serious drawback. This is most successfully 
overcome by making the thickness of the mirror not 
less than one-sixth its diameter. A few reflectors of 
great diameter have been built in France : a 4-foot 
silvered glass reflector at the observatory of Paris by 
Martin, a 3 9 -inch recently completed by the Brothers 
Henry for Meudon, and two of 32 inches' diameter 
at the observatories of Marseilles and Toulouse by 
Foucault (page 47). Before his time all reflectors 
were made of speculum metal, an alloy often composed 
of 126 parts of copper to 59 of tin. 

Amasa Holcomb, a land surveyor of Southwick, 
Massachusetts, appears to have been the earliest 
maker of telescopes in America, having begun in 
1826. Although his first instruments were refractors 
of small size, he afterward made specula as large as 
10 inches in diameter, about 30 in all. His favorite 
mounting was that known as the Herschelian type, in 
which the speculum is tilted slightly, throwing the 



Telescopes and Houses for Them 325 

image at the side of the tube, instead of centrally. 
All the light is thereby saved, but a disastrous distor- 
tion is introduced. Holcomb devised a steady and 
effective mounting, which received the award of a 
Franklin Institute medal in 1835. M r E. P. Mason: 
of Yale College, aided by his classmate Professor H- 
L. Smith of Hobart College, built in 1838 a reflector 
of 12 inches aperture, then the largest telescope in 
America; and it was used conjointly by them in 
accurate delineation of a few prominent nebulae. 

The signal success of Sir William Herschel's great 
telescopes, and the giant reflectors of Lord Rosse in- 
spired many private individuals in America as well as 
other countries to build instruments of similar design. 
Among them we mention Josiah Lyman, of Lenox, 
Massachusetts, whose 9^-inch speculum, with a system 
of supporting levers to preserve its figure when pointed 
upon stars in all altitudes, was exhibited before the 
American Association for the Advancement of Science 
at the Albany meeting, 185 1 ; and who subsequently 
figured a 12-inch speculum, now the property of 
Amherst College Observatory, by gift of his son, the 
Rev. D r Lyman of Brooklyn. As early as 1858, 
Henry Draper (page 298), returning from a visit to 
Lord Rosse at Parsonstown, constructed a 15 -inch 
speculum, the perfected result of which was a splendid 
photograph of the Moon, over 4 feet in diameter. 
Professor Brooks, now of Geneva, New York, has 
built a 9-inch reflector and used it to good advantage 
in comet work, and M r Edgecomb of Mystic, Con- 
necticut, has turned out many excellent reflectors. 
Also we must include an 18 -inch mirror ground and 
figured by Professor Schaeberle, which he used in 
planetary photography. It was an adapted Casse- 



326 



Stars and Telescopes 



grain, or type similar to the Gregorian, except that 
the secondary mirror is convex instead of concave, 
thereby producing a larger focal image. Finally, in 
1 87 1, D r Draper completed the largest reflector, of 
28 inches' diameter, yet constructed in America, 

which is now part of 
the equipment of Har- 
vard Observatory. 

Still another type of 
reflector, revived of 
late in Germany and 
by D r Common in Eng- 
land, is known as the 
6 brachy-telescope/ or 
6 oblique Cassegrain/ 
a composite of Her- 
schelian and Casse- 
grain types. The tube 
is exceptionally short, 
and the figure of the 
secondary mirror can 
be made to neutralize 
the distortion inevi- 




A. C RANYARD (1845-1894) 



tably produced by tilting the speculum. Ranyard 
devised a very ingenious type of mounting, completed 
by Professor Wadsworth and adaptable to any form 
of reflector, whereby the advantages of a stationary 
eyepiece are assured, in all possible pointings of the 
telescope. 

Next in order we outline the development of the 
refracting telescope from the beginning of the 18th 
century onward. Although Newton's experiments 
had satisfied him that a lens of short focal length 
could never be made to yield an optically perfect 



Telescopes and Houses for Them 327 

image, Euler (page 96) doubted the accuracy of 
this conclusion, and suggested that a combination of 
lenses of glass and water, of suitable curvatures, might 
produce a composite lens practically free from defects 
of color — that is, an achromatic objective. In 1733 
Chester More Hall in England was the first to 
make and use such an objective, by combining a con- 




COURSE OF RAYS THROUGH TELESCOPE 
{Objective A forms image of object at B) 

cave lens of flint glass with the original convex lens 
of crown glass. Flint glass contains much oxide 
of lead and is very dense, and its power of dispersing 
a beam of white light is about double that of an 
equal prism of crown glass, although the mere re- 
fractive powers of equal prisms of the two kinds of 
glass are the same. If, therefore, a double convex 
lens of crown glass is capped by a plano-concave or 
double concave lens of flint-glass, there is a residuum 
of refraction with the harmful dispersion effectively 
neutralized. The little diagram above shows in 
schematic fashion the passage of parallel rays from left 
to right through such a double objective, also conver- 
gence to the focal plane, and subsequent magnifica- 
tion of the image by a small eye=lens, with emergence 
in parallel pencils suited to human vision. 

It was not Hall, however, who obtained the credit 
for this signal improvement of the telescope, but John 



328 



Stars and Telescopes 



Dollond, another English optician, who secured a 
patent for the invention and reaped most of the 
benefits therefrom. No limit to the size of refractors 
now appeared to be set, save the difficulty of obtain- 
ing large disks of glass of the requisite optical purity. 
This embraces not only high transparency, and free- 
dom from air bubbles and sand-holes, but absolute 
absence of striae and waves of irregular density. So 

nearly insurmountable 
were the obstacles in manu- 
facturing flint glass that an 
achromatic of high excel- 
lence as large as 6 inches 
in diameter was unknown 
at the beginning of the 19 th 
century. 

GUINAND ( I 745-1825), 

a Swiss watchmaker, by 
patient experiment finally 
discovered how to prevent 
the heavy lead oxide from 
settling in the molten flint 
glass; and his methods, 
in some essentials secret, 
have been communicated to his successors, MM. 
Rosette & Feil of Paris, followed by M. Mantois, 
who, with Chance Brothers of Birmingham, have 
made the disks for nearly all the great refractors of 
the present day. Guinand for many years before his 
death was associated with Fraunhofer (page 17) in 
the manufacture of telescopes at Munich, and to- 
gether they produced about 1824 an achromatic re- 
fractor of nearly 10 inches aperture, with which the 
elder Struve made at Dorpat a celebrated series of 




dollond (1706-1761) 



Telescopes and Houses for Them 329 



observations of double stars. So critical was Fraun- 
hofer in his optical work, and so consummate a 
mechanician was he that a knowledge of the success 
of this great telescope finally penetrated to America, 
where at that time a permanent observatory had 
scarcely been projected. Fraunhofer, too, made 
great improvements in the equatorial telescope, by 
modifying the old parallactic stand into the German 
mounting now univer- 
sally met with, and 
only improved upon 
by the Potsdam 
mounting (page 60). 
Although David 
Rittenhouse had es- 
tablished a temporary 
observatory at Norri- 
ton near Philadelphia 
for observing the 
transit of Venus in 
1769, and the elder 
Bond (page 240) had 
in 1825 a modest pri- 
vate observatory at 

Dorchester, Massachusetts, and Yale College had in 
1832 a s -inch portable telescope of Fraunhofer's 
make, the first American observatory, intended for per- 
manent occupation as such, was erected at Chapel Hill, 
North Carolina, in the years 1831-32. Few observa- 
tions were, however, made there ; it was soon after 
dismantled, and accidentally destroyed by fire about 
1838. Olmsted (page 210) was for a brief period 
professor at Chapel Hill. General Mitchel in 1842 
visited Europe in the interest of the astronomical 




RITTENHOUSE (1732-1796) 



330 



Stars and Telescopes 



society of Cincinnati and ordered from Merz and 
Mahler, of Munich, the successors of Fraunhofer, 
a 1 2 -inch refractor. By his successful tours as a 
popular lecturer Mitchel aroused great enthusiasm 
for astronomical knowledge, and to his forceful and 
energetic personality may be traced the origin of many 
American observatories. The great comet of 1843 
led directly to the founding of Harvard College Ob- 
servatory (page 300), 
and its equipment with 
a telescope, colossal 
for that period, of 15 
inches aperture, 
which, with its twin 
companion at Pulkowa 
in Russia, formed the 
culminating labor of 
the celebrated optical 
house of Munich. 

American telescope 
builders have always 
been obliged to order 
the rough glass for 
their objectives from 
foreign makers, and 
must still do so, the few experiments in optical glass 
making outside of Europe having proved in the main 
failures. But in that fine and skilful fashioning of the 
crude lump into a perfect lens, our countrymen have 
for the last half century led the world. Fitz of New 
York made about 30 refractors, between 6 and 13 
inches aperture, many of which were subsequently 
improved by Alvan Clark; Spencer of Canastota, 
New York, whose chief success was with microscope 




ORMSBY MACKNIGHT MITCHEL 
(1809-1862) 



Telescopes and Houses for Them 33 1 

objectives, undertook telescopes also and completed 
a 13^-inch glass which the late D r Peters of Hamilton 
College (page 113) made famous by his discovery of 
48 small planets ; also Clacey of Boston and Byrne 
of New York deserve more than passing mention, not 
to say many other skilful American opticians who have 
turned out a host of telescopes of lesser dimension 
and very satisfactory performance. 

Nor have opticians of a high order been lacking 
in European countries. Cauchoix, and the Brothers 
Henry in France ; Steinheil and Schroeder in Ger- 
many ; and Cooke & Sons in England — all have 
built refracting telescopes of large aperture and excel- 
lent definition. The Henrys have constructed ten 
of the photographic objectives engaged in the astro- 
graphic survey (page 260), their mountings being by 
Gautier; also a 30-inch at M. Bischoffsheim's 
splendid observatory on Mont Gros (page 169), and 
one slightly larger for the observatory at Meudon, 
Paris. Steinheil's greatest achievement is an object- 
glass of 3i|- inches diameter for the astrophysical 
observatory at Potsdam; and Cooke's, a 2 5 -inch 
refractor now mounted at 
Cambridge, England. 
Within recent years, Cooke 
has been offering a new 
photo- visual objective, a 
triple glass said to be free TRIPLE objective (taylor) 

from the troublesome SeC- {Photographic and visual foci are 

ondary spectrum of the or- identical) 

dinary double objective, and 

to converge visual and photographic rays to an iden- 
tical focus. The curves are the work of M r H. D. 
Taylor, and the glass employed is known as the new 




332 Stars and Telescopes 

Jena glass, made from the formulae of Professor Abbe 
of the University of Jena, who conducted a course 
of experiments under the auspices of the German 
government. 

The secondary spectrum gives rise to an effect 
which becomes especially harmful in very large 
objectives, surrounding all bright stars and planets 
with a brilliant bluish luminosity, greatly interfering 
with the observation of faint adjacent objects like 
satellites and companion stars. This difficulty is in- 
herent in the glass itself, because dispersion or de- 
composition by the crown glass cannot be exactly 
neutralized by the recomposition of the ordinary 
flint. With the Jena glass, however, D r Hastings of 
Yale University has succeeded in producing a double 
objective practically free from secondary spectrum 
effect, by careful investigation of the theoretical cur- 
vatures, and placing the flint lens on the outside of 
the combination, so that the light passes through it 
before reaching the crown. 

The curves of the lenses in achromatic objectives 
have occasioned much research in theoretical optics, 
and many different constructions have been evolved, 
among them that of Littrow, with the crown double 
convex and the flint plano-concave. Gauss (page 99) 
devised a form in which the crown is plano-convex 
and the flint concavo-convex. In the type of objec- 
tive preferred by Clark, the crown is double convex, 
and the flint double concave, the two lenses being 
mounted in a long cell with a space between them 
equalling about £ their diameter. This construction 
adds to the weight of the mounted objective, but 
affords better correction of the aberration, permits 
easy cleaning of the inner faces, and allows free circu- 



Telescopes and Houses for Them 333 

lation of air between flint and crown. In all these 
types the light reaches the crown lens first. 

Before passing to a consideration of the remarkable 
series of telescopes built by the Clarks, the excellent 
work of Sir Howard Grubb must be further specified, 




27-INCH VIENNA EQUATORIAL 
{Built by Sir Howard Grubb) 

embracing a 27-inch telescope complete (illustrated 
above), and mounted at the Imperial Observatory of 
Vienna, one of the best equipped establishments of 
Europe. Also he has constructed a 26-inch visual and 
a 28-inch photographic objective for the Royal Obser- 
vatory at Greenwich, as well as numerous glasses of 
smaller aperture ; and his mountings are especially 
commended for rigidity. A type of clock-motion 



334 Stars and Telescopes 

with electric control devised by Grubb permits the 
close following of a star in its diurnal motion, with 
that degree of accuracy necessary to secure circular 
star-images on a photographic plate during long 
exposures. 

Of all makers of telescopes Alvan Clark attained 
the greatest celebrity. A portrait painter in Boston 




THE IMPERIAL OBSERVATORY AT VIENNA 
(Dr Edmund Weiss, Director) 

in 1844, accident drew his attention to the construc- 
tion of a small reflector, the success of which led to 
his making refractors. Two years later he was estab- 
lished in the business of telescope construction with 
his two sons, Alvan Graham (page 285) and George 
Bassett. Clark's first refractors were introduced to 
astronomers by Dawes (page 283) who purchased 



Telescopes and Houses for Them 335 



five of them, and subjected them to the most critical 
tests. Above the aperture of 6 inches, the Clarks 
made in all about 75 objectives, with mountings for 
the most of them. Their objectives are optically 
more perfect than the 
atmosphere in which they 
can generally be used, 
bearing a hundred di- 
ameters of magnifying 
power for each inch of 
aperture, and separating 
the components of close 
•double stars up to the 
limit set by Dawes's em- 
piric formula. Clark 
telescopes have not only 
a world-wide fame but a 
world-wide distribution. 
Between i860 and 1892 
the Clarks were five 
times called upon to 

construct ' a telescope more powerful than any now 
in existence ' ; and each time the advance was from 
■one to six inches in excess of the aperture of the then 
greatest glass. These were, in order, the 18-J-inchnow 
at Evanston ; the 26-inch at Washington, a duplicate 
of which was built by them for the University of Vir- 
ginia ; the 30-inch for the Imperial Observatory at 
Pulkowa, near Saint Petersburg ; the 36-inch for the 
Lick Observatory; and the 40-inch, still the largest 
refracting telescope in the world, for the Yerkes Obser- 
vatory of the University of Chicago. Among other 
great refractors of their construction are a 2 3 -inch for 
Professor Young at Princeton, and a 24-inch for M r 




ALVAN CLARK (1804-1887) 



336 



Stars and Telescopes 



Percival Lowell, now mounted in his private obser- 
vatory at Flagstaff, Arizona. This glass and the Yerkes 
obj ective were the last work of Alvan Graham Clark,. 
his constant co-worker being M* Carl Lundin, an 
able optician who has served a quarter-century ap- 
prenticeship under all the Clarks, and now continues 
the work of the firm at Cambridgeport. 




GEORGE B. CLARK (1827-1891) 



The Lick 3 6 -inch lenses are mounted in a cast- 
iron cell faced with inlaid silver where the glasses- 
rest against it. The weight of the objective in its- 
cell is about 700 pounds, and its cost was $53,000. 
An additional lens, or photographic corrector of 33. 
inches aperture, was provided at a cost of $13,000. 
The focal length of the visual object-glass is 56 feet;. 



Telescopes and Houses for Them 337 

48 feet when the photographic corrector is applied. 
The Yerkes objective weighs about half a ton, and its 
crown lens is three inches thick at the centre. The 
total cost of this telescope, inclusive of its mounting 
was about $125,000. v 

Alvan Clark was in 1867 awarded the Rumford 
medal of the American Academy of Arts and Sciences 
for the perfection of his optical surfaces. The com- 
pletion of the 30-inch Russian object-glass brought the 




YERKES OBSERVATORY OF THE UNIVERSITY OF CHICAGO 

{Located on the shore of Lake Geneva, Williams Bay, Wisconsin. This 
observatory contains the largest refracting telescope in the world, was 5. 
years in building, and cost about $500,000, the gift of Mr Chas. T. Yerkes) 



Clarks the signal honor of the golden medal of the 
Empire, conferred for the first time by Alexander 
the Third. 

Second in importance only to the objective of a 
telescope are the mounting by which it is pointed to- 
ward the heavenly bodies, and the eyepieces with 
which the images formed by it are examined. The 
mountings made by the Repsolds of Hamburg 
are unsurpassed, their largest having been con- 
structed for the 30-inch Clark glass at Pulkowa 
(Page 133). 

S & T — 22 




40-INCH TELESCOPE OF THE YERKES OBSERVATORY 

*(Glass by Mantois, objective by Alvan Clark &> Sons, of Cambridge fiort, mounting by 
Warner & Swasev of Cleveland. The tube is about 65 feet long ; and, although the -mov- 
ing parts of this great telescope weigh nearly 15 tons, the whole is easily managed by one 
man, through control of several electric motors. The counter-weighted dome-floor rises and 
Jails zzfeet, on the plan origi7iated by Sir Howard Grubb. The photograph shows it near 
its lowest position. The dome is qofeet in diameter, and weighs 140 tons) 



Telescopes and Houses for Them 339 

Repsold has many foreign rivals who have con- 
structed mountings for smaller instruments. Especially 
may be mentioned Secretan of Paris, Bamberg of 
Berlin, Heyde of Dresden, and Salmoiraghi in Italy. 
In America, Saegmuller has made fine mountings, 
one of his largest for a 20-inch glass at Manila. 
Warner & Swasey of Cleveland have met with marked 
success in the larger mountings. Among their im- 
provements are devices for all necessary manipulations 
of the telescope from the eye end; incandescent 
lamps for illuminating the circles ; wheels and circles 
for ' setting ' in both co-ordinates from the dome- 
floor 1 and the adoption of ball-bearings to give ease 
of motion to the massive steel axes which, in their 
mountings for the Lick and Yerkes objectives, weigh 
from 1 to 3J- tons each. The Lick mounting cost 
842,000, and the Yerkes about 360,000. The latter 
is provided with an elaborate system of electric 
motors, which do the work of clamping and give quick 
motion to the telescope on either axis as required. 
Also the dome is turned in either direction, and the 
floor of the dome elevated or depressed by electric 
power. 

The modern American mountings provoke little 
unfavorable criticism. In some classes of observation 
difficulties arise from their lack of rigidity, both as to 
the axes themselves and the iron-work supporting 
their bearings. Too great care cannot be expended 
upon the founding and construction of the pier upon 
which the mounting rests. In general, our mountings 
are surpassed in rigidity by those of like dimension 
from the best English and Irish shops. But if the 
American telescope is compared with those of foreign 
makers, in point of subsidiary apparatus for its con- 



340 



Stars and Telescopes 



venient working, we find a constantly growing dispo- 
sition on the part of the instrument builder to consult 
the wants of the astronomer and to profit by his. 
suggestions. 

A convenient form of mounting known as the 
equatorial coude, or < elbow equatorial/ was invented 
in 1882 by M. Loewy, now director of the Paris Ob- 
servatory. As the illustration shows, the instrument 




THE EQUATORIAL COUDE (DESIGNED BY LOEWY) 

(The observer sits in a comfortable room, his telescope being mou?tted in the 
open air) 



itself is mounted in the open air, while the observer, 
as if working with a microscope, sits always in a fixed 
position, no matter what the direction of the object he 
may be observing. He may therefore avail himself 
of comfortable temperatures. Easy and rapid hand- 
ling, too, are very advantageous, as well as the attach- 
ment of cameras and spectroscopes. There are dis- 
advantages, of course, chiefly the loss of light by 



Telescopes and Houses for Them 34 r 

reflection from two plane mirrors set parallel at an 
angle of 45 ° to the declination and polar axes. The 
objective is mounted in one side of the upper cube 
which, with its mirror also, turns round on the decli- 
nation axis. The long oblique tube is itself the polar 
axis, at the upper end of which the observer sits, and 
a powerful clock carries the instrument slowly round 
to follow the stars in their diurnal motion. First cost 
of the equatorial coude exceeds that of the ordinary 
equatorial, but the expense of a dome is mostly saved, 
as the coude - is housed under a light rolling structure. 
This type of instrument, although not yet represented 
in America, has many examples in the observatories of 
France. With the larger one at the Paris observatory, 
built by the brothers Henry, was taken a remarkable 
series of lunar photographs, now combined into a 
complete atlas of the Moon. Two of these are well 
reproduced in Chapter in (pages 29 and 31.) Defi- 
nition in the coud£ is excellent, and surface deteriora- 
tion of the silvered mirrors is not troublesome. 

Quality of the ocular or eyepiece is a factor of 
great importance in the performance of an objective. 
The character, field of view, and power of eyepieces, 
should be carefully suited to the nature of the tele- 
scopic work. The ordinary forms are the positive or 
Ramsden eyepiece (used for micrometers and all 
kinds of astronomical instruments requiring a reticle), 
and the negative or Huygenian eyepiece (usually em- 
ployed for gazing work merely) . It is essential that 
the eyepiece should be achromatic as well as the ob- 
jective. The Steinheil monocentric eyepiece is a 
triple glass, achromatic, and composed of two flint 
menisci of different thicknesses capping a double con- 
vex crown on both sides. The performance of this 



342 



Stars and Telescopes 




ocular is especially good on stars and planets. Direct 
observation of the sun requires a polarizing eyepiece, 
or helioscope, best made in this country by Brashear. 
It reduces the intense solar light and heat to a degree 
not harmful to the delicate tissues of the eye. 

The micrometer is an accessory of the telescope 
used in the measurement of small arcs or angles. It 
is attached in place of the ordinary 
eyepiece by means of an c adapter/ 
or draw- tube. In the field of view 
are at least three wires, or threads, 
or spider-lines, as in the illustration 
adjacent. By turning the microme- 
ter screw the two parallel threads 
are separated until the space to be 
measured, as the diameter of a 
planet, is just embraced between 
these two lines. The divided head 
of the micrometer screw and a 
scale adjacent record the number 
of whole revolutions and fractional 
parts ; and this is readily converted 
into arc, because the arc value of one revolution is 
easily ascertained by observations upon stars. At 
night the micrometer lines are rendered luminous by 
light from a small electric lamp (at the left in the 
opposite illustration), or an adjustable oil lamp shown 
below it. A micrometer will usually be provided with 
a separate equipment or battery of eyepieces, ranging 
in power from about 9 to 90 for each inch of aperture 
of the object glass with which they are used. The 
illustration represents the micrometer of the 36-inch 
Lick telescope, constructed by Saegmuller. For 
about ten years it has been kept in nearly constant 



"ST 



MICROMETER 

{Screw S moves thread 
bb relatively to sta- 
tionary horizontal 
thread f a certain 
number oj revohitions 
which are read from 
graduated head K at 
index s) 



Telescopes and Houses for Them 343, 

use, notably by Professor Burnham in the discovery 
and observation of very faint or close double stars* 
A similar instrument of unusual proportions was. 
built by Warner & Swasey for the 40-inch Yerkes, 
telescope. 

In considerable part the observations, particularly 
of larger arcs, formerly made with the micrometer, are 
now supplanted by the greater accuracy attainable 




a modern micrometer 

{With battery of eyepieces, oil and electric lamps, etc.) 

with the heliometer (page 277) ; but more especially 
the photographic plate and measuring engines are re- 
placing both. As early as 1850 the younger Bond 
obtained with the 15 -inch Harvard telescope, fine 
photographic impressions of Vega, and later of the 
double star Castor, showing an elongate disk. This was 
the beginning of stellar photography. Bartlett, at 
West Point, and Campbell, in New York, secured 
good pictures of the annular eclipse of 26th May> 



344 



Stars and Telescopes 



-s^--^ 




1854, the first celestial phenomenon photographically 
observed. By measuring his plates of Mizar, Bond 
in 1857 proved photography capable of results equally 
precise with direct observation of stellar images. The 
year following, Rutherfurd of New York undertook 
celestial photography at his private observatory with 

an objective of 11 \ 
inches aperture fig- 
ured by himself. 
Plates prepared by 
the old wet collodion 
process were used, and 
exposures of 5 to 10 
seconds brought out 
the belts of Jupiter, 
and even Saturn's ring. 
In 1863, Rutherfurd 
began the construction 
of the first objective 
figured solely for pho- 
tographic rays, and he 
obtained the required 
actinic correction by 
means of his neat 
adaptation of the spectroscope in examining the chro- 
matic condition of an objective. So great was the 
improvement that an exposure of one second gave an 
image of Castor, which required ten seconds in the un- 
corrected telescope. Rutherfurd later demonstrated 
the feasibility of converting any visual objective into 
a nearly equivalent photographic telescope by mount- 
ing in front of it a meniscus of flint glass. In 1869 
he constructed the first instrument of this character, 
13 inches in aperture, and with it were taken, in 



RUTHERFURD (1816-1892) 



Telescopes and Houses for Them 345 

August, 18 7 1, the first photographs of the sun, show- 
ing the minute granulations of its surface. His pictures 
of sunspots have not yet been surpassed (page 52), 
and his lunar photographs compare favorably with 
recent work at Paris and Mount Hamilton. 




THE 40-FOOT HORIZONTAL PHOTO-HELIOGRAPH 
{As mounted at the author's eclipse station in Japan, 1887) 



The transits of Venus, in 1874 and 1882, offered 
exceptional opportunities for the application of pho- 
tography, and a type of instrument known as a 'hori- 
zontal photo-heliograph/ originated by the elder 
Winlock in 1869, was brought into service by the 



346 Stars and Telescopes 

American Commission, whose work was directed in 
the main by Professor Newcomb. The Clarks built 
eleven of these instruments, eight for the Government, 
and one each for the Princeton, Harvard, and Lick 
observatories. They have photographically corrected 
objectives 5 inches in diameter, and of 40 feet focal 
length ; are mounted in the meridian, and the sun's 
rays are thrown constantly through the objective by 
7-inch plane mirrors, suitably mounted and driven by 
clock-work. In 1888, Brashear built a similar in- 
strument for the Imperial Observatory of Japan at 
Tokyo. Besides the large scale of the original image, 
the sun appearing about 4§ inches in diameter on the 
plate, the stationary image and plate-holder allow the 
photographer to avail himself of any required number 
of assistants, all of whom work within the dark room, 
which thus replaces the moving camera as ordinarily 
employed in celestial photography. The preceding 
illustration represents one of the American photo- 
heliographs as mounted by the writer at Shirakawa, 
Japan, for the total eclipse of 1887. On the right are 
mirror and objective, and in the background the 
photographic house, the 40-foot tube between them 
being housed from the direct rays of the sun. With 
similar instruments Professor Schaeberle in 1893, in 
Chili, and Professor Campbell in 1898, in India, ob- 
tained very fine pictures of the sun's corona, — not, 
however, by using the mirror, but by rigidly fixing the 
objective high in the air, and following the sun's mo- 
tion with a slowly-moving plate-holder. 

As it is not our present purpose to trace the history 
of astronomical photography, but only to outline salient 
departures, we mention but a few additional develop- 
ments. Most interesting of all is the train of cir- 



Telescopes and Houses for Them 347 

cumstances leading up to our modern methods of 
determining star places by photographic means. 

On the early morning of the 8th September, 1882, 
M r Finlay, first assistant at the Observatory of the 
Cape of Good Hope, discovered and first observed 
a bright comet in Hydra (page 200). Several photo- 
graphers in South Africa obtained photographic im- 
pressions of the new comet within a month following, 
by the use of ordinary apparatus only; and on re- 
porting this fact to D r Gill, he at once began to take 
photographs of the comet, with the assistance of M r 
Allis of Mowbray, whose only suitable lens was a Ross 
doublet, but 2 \ inches in diameter, and of 11 inches 
focal length. They not only succeeded in taking fine 
pictures of the comet, but their plates on develop- 
ment showed hundreds of stars, well defined over an 
area so large as to suggest at once the practicability 
of employing similar and more powerful means for 
the construction of star maps. Admiral Mouchez, 
late director of the Paris Observatory, endorsed the 
views of D r Gill, and his encouragement of the 
Brothers Henry led them to devote their attention to 
the construction of suitable lenses. As D r Gill well 
says, t The brilliant results which Messrs. Henry soon 
attained are still fresh in the minds of astronomers, and 
mark an epoch in the history of astronomy in the 
nineteenth century.' One of these is the remarkable 
photograph of the Pleiades, already shown on page 
237. Meanwhile D r GiLL himself went zealously for- 
ward with the work of star charting by means of a 
6-inch Dallmeyer lens, the photographic work being 
done by M r Woods at the charges of the Government 
Grant Fund of the Royal Society. 

The plates have all been measured by Professor 



348 



Stars and Telescopes 



Kapteyn with a parallactic apparatus of his own de- 
vising, dependent upon the following principle : hold 
up against the sky a photographic negative of the 




PLATE-MEASURING ENGINE 
{Designed and built by the Repsolds) 



-same region, taking care to keep it perpendicular to 
the line of vision through the center of the plate; 
then if it be removed from the eye to a distance 
equal to the focal length of the lens, every star can be 



Telescopes and Houses for Them 349 

-exactly covered by its dark image on the negative. 
Then by substituting for the eye an instrument suit- 
able for measuring stellar positions in the sky, their 
positions are quickly read off from the plate itself. This 
ingenious apparatus is quite different from the ordi- 
nary plate- measuring engine, shown opposite, with 
which stellar photographs are usually converted into 
•catalogue positions. This instrument measures merely 
plane co-ordinates, while that of Professor Kapteyn 
measures spherical co-ordinates, as the geometer des- 
ignates them. The completed catalogue of stars of 
the southern firmament, the joint research of D r Gill 
and Professor Kapteyn, a work of enormous magni- 
tude, is now appearing in the Annals of the Cape 
Observatory, As a result of D r Gill's initiative came 
also the Astrographic Congress (p. 260), with its 
comprehensive plans, and more than a dozen photo- 
graphic telescopes at work for years in both hemi- 
spheres — all as a direct issue from one comet and a 
few nearly accidental photographs of it taken in re- 
motest Africa. 

Meanwhile, but quite independently, stellar photo- 
graphy had been making rapid progress in America. 
Professor Pickering, employing at first very small 
photographic instruments of the ordinary type, ex- 
tended his researches by means of an 8-inch Voigt- 
lander lens, refigured by Clark, and since known as 
the Bache telescope (page 299). The star charts 
taken with this instrument in Cambridge and Peru, 
and with its duplicate, the Draper telescope, have 
yielded results of high importance ; not only in the 
determination of stellar magnitudes, but, by affording 
the means of studying certain regions of the sky at 
.-many different epochs, they have brought to light 



3SO 



Stars and Telescopes 



many new stars. But their use as spectroscopes has 
secured the greatest contribution to stellar astronomy 




VARIABLE NEBULA SURROUNDING ETA CARINAE (ARGUS) 
{Photographed with the i^-inch Boy den telescope) 

(pages 297-301). By mounting prisms in front of 
the objectives, on the plan first tried by Fraunhofer 



Telescopes and Houses for Them 3 5 1 

in 1823, all stars in the field impress their spectra, 
sometimes as many as 1,000, on a single plate. 

The requisite width of spectrum is given by mount- 
ing the prism with its edge east and west, and suitably 
varying the clock-motion from the true sidereal rate, 
according to the degree of dispersion employed, as well 
as the color and magnitude of the stars in the photo- 
graphic field. These researches have culminated in 
the construction and use of the Bruce telescope, al- 
ready described and illustrated (pages 263-265), and 
which has fully met the successes predicted for it. 
Its enormous power is readily inferred from the fact 
that on a single plate 14 X 17 inches were counted no 
less than 400,000 stars. This extraordinary result is 
a necessary consequence of the great aperture of the 
lens with a relatively short focal length, a combination 
which photographers designate by the term c quick- 
acting.' The rapidity of lenses of the doublet type 
may be inferred on comparison of the 8-inch Bache 
telescope of 44 inches focal length with the standard 
13-inch astrographic telescope of 134 inches focus; 
the former requires but an hour's exposure to record 
a star of the 14.7 magnitude, while the latter consumes 
three hours in impressing the same image. 

During the progress of this work Professor Picker- 
ing devised a novel form of double objective which is 
equally efficient for both photographic and optical 
work. This long-sought result is obtained by figuring 
the two faces of the crown lens very different in curva- 
ture, and modifying the cell so that the flint lens may 
be moved toward the focal plane when desired. For 
visual observations the two lenses are in contact, the 
more convex surface of the crown lying next to the 
concave face of the flint. By reversing the crown lens 




hale's type of spectro-heliograph 

(Constructed by Brashear) 



Telescopes and Hoitses for Them 353 

and separating the flint three inches from it, the com- 
bination becomes an objective perfectly corrected for 
the actinic rays — or nearly so. The fact, however, 
seems to be that there is a trifling sacrifice of quality, 
in both the optical and the photographic combination, 
for the sake of this convenient and inexpensive union 




UNIVERSAL SPECTROSCOPE BY BRASHEAR 

{Arranged for visual work. Light enters the spectroscope at the extreme 
left, passes through the prisms or is reflected from the grating in the 
flat-topped box at the right, and comes to the eye which is placed at the 
eyepiece on the micrometer in the middle of the engraving. Below it are 
the tube and piateholder, which are substituted when spectra are to be 
photographed) 

{By special permission of the American Book Company) 



of two objectives in one. A 13-inch telescope of this 
pattern was made by the Clarks, with which the fine 
photograph of 77 Carinae was taken (page 350), and a 
construction practically identical was independently 

S & T — 23 



354 Stars and Telescopes 

invented by Sir George Stokes. The 28-inch Green- 
wich lens figured by Sir Howard Grubb is an example 
of this type. 

The reflectors built by M r Brashear have been de- 
scribed earlier in this chapter. But his mechanical skill 
and untiring energy have enabled him to play a most 
important role in the recent progress of physical as- 
tronomy. His optical surfaces exhibit the last order 
of precision and finish ; and many are the physicists 
and astronomers whose work has been facilitated by 
his deft constructions. Principally by spectroscopes 
(page 353) has his reputation been enhanced, and he 
has built the largest instruments of this character ever 
constructed, among them the Lick spectroscope (page 
288), and one for the Yerkes telescope. Also Pro- 
fessor Hale's lesser spectro-heliograph, illustrated on 
page 352, is M r Brashear's workmanship, and the 
work accomplished with it has already been described 
•on pages 63-65. 

Likewise, M r Brashear has achieved great success 
in figuring objectives, both optical and photographic. 
His largest object-glass is of 18 inches aperture, and 
it acquired instant fame from its use by M r Perctval 
Lowell and his assistants in observing Mars, at Flag- 
staff, Arizona, during the opposition of 1894. This 
glass is now mounted at the Flower Observatory of 
the University of Pennsylvania. Photographic ob- 
jectives of all sizes have come from M r Brashear's 
competent hands — the 6-inch Willard lens (ordi- 
nary portrait), re-figured for Professor Barnard, with 
which, at the Lick Observatory, he obtained his un- 
surpassed photographs of the Milky Way ; an 8-inch 
for Professor Terao, of Tokyo ; a 10-inch for the 
Yerkes Observatory; and a pair of 16-inch doublets 



Telescopes and Houses for Them 355 



for D r Wolf, of Heidelberg, used to excellent advan- 
tage in the photographic discovery of small planets 
(page 115). The adjacent illustration is reproduced 
from that part of a photographic plate on which was 
discovered a small planet ; it shows as a faint elongate 
trail, indicating the amount of 
its motion during the exposure 
of two hours. Perhaps the best 
form of mounting for short- 
focus cameras of this descrip- 
tion is that shown in the 
reproduction on p. 35 7, from a 
design by Heyde of Dresden, 
for the observatory at Moscow. 
It readily admits of the neces- 
sarily long exposures without 
reversal from one side of the 
pier to the other. 

As the telescope and its 
accessories become very large 
and massive, the disadvan- 
tages of the Fraunhofer or Ger- 
man mounting become more 
and more pronounced, on ac- 
count of the overhang of the 
declination axis, and its flexure, 
as well as the hindrance of the pier itself, preventing 
very long exposures or periods of observation, except 
by reversal of the telescope to the opposite side of 
the pier. So there is a present tendency to revert to 
the old type of parallactic stand first invented by 
Romer and now universally known as the English 
mounting, in which the polar axis is supported at its 
upper end by a second bearing and pier, and the axis 




DISCOVERY OF A SMALL 
PLANET 

{by photography. The planet is 
the long object at the centre) 



356 Stars and Telescopes 

itself is a double fork with the telescope swung between 
its prongs. Of this type is the old equatorial mount- 
ing at Greenwich devised by Sir George Airy. The 
chief disadvantage is that the sky close around the pole 
and underneath it is inaccessible ; but this is more than 
counterbalanced by the cardinal advantage of having 
the entire space beneath the polar axis free and clear, 
so that a celestial body can be followed from one 
horizon to the other without reversal of the instrument. 
Several of the astrographic telescopes were mounted 
in this fashion; also in 1898 the reflector of one 
metre aperture at the observatory at Meudom The 
clock-motion is imparted with great steadiness, and 
the general design of the English mounting permits a 
very satisfactory solution of the engineering problems 
that arise in the construction of great telescopes. 
This type of mounting received the mature approval 
of Alvan Graham Clark. 

With M r Brashear is associated D r Hastings of 
Yale University, who calculated the curvatures of all 
the objectives fashioned by the former in recent years. 
D r Hastings is himself a practical optician as well as 
theoretical physicist, having made many objectives 
with his own hands. The largest has an aperture of 
9.4 inches, and is mounted at the Johns Hopkins Obser- 
vatory. Contrary to the usual practice of opticians, no 
examination of the quality of image formed by the 
lens was made until the work upon it was finished ; and 
on first trial the objective was found so nearly satis- 
factory that only twenty minutes were required to ren- 
der it sensibly perfect. In this achromatic glass, with 
the flint lens in advance of the crown, with a space 
of o in .i between them, a variation of this latter dis- 
tance will effectively correct the objective for changes 



Telescopes and Houses for Them 357 

of temperature. The curves of M r Brashear's ob- 
jectives being based on the formulae of D r Hastings 
there is a close agreement of the actual focal length 




A MODERN CAMERA FOR STELLAR PHOTOGRAPHY 
( With equatorial mounting designed by Heyde) 



with the calculated value, which is often a marked 
advantage. 

The effect of focal length upon the performance of 
a lens is excellently shown by the wonderful photo- 



358 Stars and Telescopes 

graphs of the Milky Way recently obtained by Pro- 
fessor Barnard with a magic-lantern lens of i \ inches 
diameter, and 5^- inches focus. In a few minutes'' 
exposure it photographs what the ordinary quick- 
acting portrait lens requires several hours to show- 
The scale is of course very small, and the cloud-forms, 
of the Galaxy are so compressed that they act, not 
as an aggregation of individual stars, but as a surface. 
The earth-lit portion of the Moon was well depicted 
by exposure of a single second ; the brighter cloud- 
forms of the Milky Way appeared in ten to fifteen 
minutes; and a great wing-like nebula involving 
v Scorpii was discovered by Professor Barnard with 
this simple lantern lens. 

The recent application of photography to the 
trails of meteors is very suggestive. Lenses of short 
focus and a large field of view are best. Professor 
Barnard, on the 13th November 1893, obtained the 
opposite photograph of a meteor which shot across 
the field while he was making an exposure more than 
two hours in duration in order to secure the faint 
comet below (comet iv, 1893). But a still more 
remarkable delineation has been secured : on the 18th 
June 1897, when the Bache telescope at Arequipa 
was photographing spectra of the stars in the con- 
stellation Telescopium, a bright meteor flashed across, 
the field, and the lines of its spectrum were there- 
fore registered upon the plate — the first spectrum 
of a meteor ever recorded by photography. There 
were six lines, and their intensity varied in different 
parts of the photograph, showing a change in char- 
acter of the meteor's light as its image trailed across 
the plate. The lines were mostly due to hydrogen, 
resembling stars that have bright line spectra. Thus 




METEOR-TRAIL PHOTOGRAPHED AT THE LICK OBSERVATORY, 13 November 1893 

{By Professor Barnard with 6-inch Willard lens. Exposure 2^ 5m upon stars and the faint 
object below y comet iv 1893) 



360 Stars and Telescopes 

the chance spectrum of this meteor will, Professor 
Pickering hopes, aid in ascertaining the conditions 
of temperature and pressure in such stars. The ex- 
pected mid-November meteoric showers of 1899 an d 
1900 will undoubtedly yield further and similar re- 
sults. These, with trails from D r Elkin's multiple 
cameras ( page 212) will probably provide data for a 
more accurate orbit of the Leonids. More than thirty 
were photographed in November 1898. 

An arrangement of multiple cameras for observa- 
tion of total solar eclipses was first worked out by 
the writer in 1889, for the eclipse of the 2 2d De- 
cember in West Africa. . In all, 23 instruments, chiefly 
photographic, were attached to a massive polar 
axis, and pointed parallel to each other, following 
accurately on the eclipsed Sun. The engraving oppo- 
site illustrates many of them ; also in the foreground 
are the pneumatic contrivances by which exposing 
shutters, plate-holders, and all other moving devices 
for eclipse observation were operated automatically. 
The control was effected by a perforated strip of 
paper, similar to the music sheets now commonly 
used in automatic organs. Each perforation in the 
eclipse^ sheet represented, not a musical note, but a 
mechanical movement of some particular device. 
By the liberality of M r D. Willis James of New York, 
a trustee of Amherst College, a similar battery of 
instruments was duly installed in Yezo by the Am- 
herst Eclipse Expedition in 1896. One of the nu- 
merous devices was constructed with reference to 
securing on a single plate the imprint of a few coro- 
nal streamers complete in their entire length. This 
had never been done, because exposure long enough 
to give the outer corona burns out the film where the 




THE PNEUMATIC COMMUTATOR AND PHOTOGRAPHIC BATTERY OF 

ECLIPSE INSTRUMENTS (TODD) 

(As mounted at Cape Ledo, African/or the total eclipse of December 1889) 







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Telescopes and Houses for Them 363 

bright inner corona would otherwise be. In the de- 
vice illustrated opposite, three concentric rings and a 
central disk are removed from the photographic field 
successively, permitting long exposure for the outer 
and short for the inner corona. 




THE ELECTRIC COMMUTATOR (TODD) 
{Amherst Eclipse Expedition to Japan , 1896) 

Instead of pneumatic operation, the necessary move- 
ments, about 500 in all, were secured at the critical 
instants by the control of an electric commutator 



364 



Stars and Telescopes 



% 
\ 









N 



(preceding page). The pneumatic and electric sys- 
tems both worked perfectly ; but clouds at both sta- 
tions unfortunately ob- 
scured the corona. 
The ease with which a 
number of delicate 
pieces of photographic 
apparatus can be ar- 
ranged, the certainty 
with which they can be 
operated ; the large num- 
ber of photographs ob- 
tainable by this means 
for subsequent study, the 
dispensing with manual 
movements during total- 
ity when every nerve is 
at high tension — all 
point to the desirability 
of repeating the experi- 
ment during the coming 
eclipses of 1900 and 
1 90 1. Also the novel 
device of M r Burckhal- 
ter, for obtaining the 
bright inner and faint 
outer corona on the same 
plate by means of a suit- 
ably shaped and swiftly 
whirling vane, revolving 
in the photographic field 
during exposure, was sue-, 
cessful during the India 
eclipse of 1898, and is 
worthy of permanent 




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Telescopes and Houses for Them 365 

adoption in eclipse programmes of the future. But 
even more important is the photography of the flash 
spectrum, near beginning and end of the total phase. 
The unobscured limb of the' Sun is then a very slen- 
der crescent; and by using the objective prism, or 
prismatic camera, the developed image on the plate 
comes out as in the opposite photograph — not a 
single crescent, but a succession of crescents whose 
position and size enables us to say to what substances 
the light owes its origin, and to study the depth of 
the reversing layer all around the Sun's edge. The 
total eclipses of 1896 and 1898 indicate that the 
depth of this stratum is about 700 miles. 

The advances of astronomy by the aid of pho- 
tography are too numerous for further treatment 
here. In 1840 the Moon was first photographed^ 
in 1850 a star, in 1854 a solar eclipse, in 1872 the 
spectrum of a star, in 1880 a nebula, in 1881 a comet,, 
in 1897 the spectrum of a meteor, and in 1898 a 
stellar occultation by the Moon. All these epoch- 
making photographs were made in America. Nearly 
every branch of astronomical science has been ad- 
vanced by the instrumentality of photography, so- 
universal are its applications, and so persistently have 
they been put to the successful test. 

Before passing to the construction of observatories 
and suitable sites for them, one or two paragraphs 
will be devoted to the instruments of the old astron- 
omy, or astronomy of precision, as it is often termed. 
Most important of all is the meridian circle, the joint 
invention of Romer and Picard, before whose day the- 
position of a star or planet on the celestial sphere was 
observed by means of a quadrant. Hevelius con- 
ducted a long and valuable series of observations with 



366 



Stars and Telescopes 



an instrument of this sort, illustrated adjacent; but 
they were unfortunately destroyed by fire at Dantzig, 
the scene of his labors. Two persons were neces- 




HEVELIUS AND HIS CONSORT OBSERVING 

(The instrument is a quadrant of the i-jth century, before 

telescopes were adapted to measurement of angles) 



sary to make a complete observation, and the star's 
direction was fixed, not by the telescope, but by sights 
or pinules. A surprising degree of accuracy was 
reached by carefully repeated measures. 



Telescopes and Houses for Them 367 

From the middle of the 17th century onward, we 
must omit the intervening forms of arc- measuring 
instruments, down to the end of the 19th century, 
when we find astronomers almost universally employ- 
ing the meridian circle. An excellent type by the 
best modern maker is shown on the following page, 
by courtesy of Professor Payne, editor of Popular As- 
tronomy, an American monthly that provides much 
information about all kinds of astronomical apparatus, 
including telescopes, their manufacture, and use. As 
its name implies, the meridian circle revolves in a verti- 
cal plane north and south ; and its construction de- 
mands a house with a sliding or removable roof, with 
shutters opening below it, as at the extreme left in 
the illustration. A clear strip of sky is thereby ac- 
cessible for observation in every part, and unobstruct- 
edly free from the zenith down to the north and 
south horizons. The exterior of a meridian room is 
shown in the left-hand wing of D r Roberts's observa- 
tory, page 290. 

Within a meridian room the telescope, whether a 
transit instrument or a meridian circle, surmounts two 
stable piers, between which it turns round on bear- 
ings called Y's. Circles adjacent to the telescope, 
and on either side of it are rigidly attached to the 
horizontal axis ; and they, with both telescope and axis 
turn round as a unit, the axis of the telescope describ- 
ing the plane of the meridian. The circles enable 
any known star to be found, by means of its distance 
from the zenith. Then the time of its passing the 
wires in the reticle is observed by a clock or chronom- 
eter, usually with the aid of a chronograph which 
electrically records the precise instants at which the 
transits take place. If a star's position on the celes- 




< 

H 

O 
in 
W 



P* 

O 
H 

> 



n 

o 
w 

o 
u 

o 

H 

w 
•J 

< 



w 
Q 

►J 

O 

p* 
w 

w 
X 
H 






^ 



I 



•& 
k 



5 

•8 

5 



Telescopes and Houses for Them 369 

tial vault is already known, one complete meridian 
observation provides the means of finding the latitude 
of the observatory, and the local time ; or conversely, 
if these elements have previously been found, a com- 
plete observation enables us to assign the star's exact 
geometric position on the celestial sphere ; in other 
words, we determine its right ascension and declina- 




AUTOMATIC DIVIDING-ENGINE 
{For graduating circles. Built by Secretan of Paris) 

tion, as technically called. Meridian instruments of 
high precision and excellent workmanship are con- 
structed in America as well as in Europe. Buff & 
Berger of Boston, Saegmuller of Washington, and 
Warner & Swasey of Cleveland, are the chief mak- 
ers. Accurate division of their circles is the chief 
difficulty of construction, but this end is now attained 
s & t — 24 



37° 



Stars and Telescopes 



with all necessary precision by means of graduating 
engines, similar to the one in the last illustration. 
Errors of a whole second of arc in the position of a 
line on the face of a silver circle are now uncommon 
in the best modern instruments. This means that of 
all the lines automatically engraved on a fine circle 20 
inches in diameter, one is rarely misplaced by so much 
as the half of T q ^ ^ of an inch. 




zach (17 54-1832) 

But few observers are able to assign the absolute 
time when a star is actually crossing a line in the field 
of view : most will record the instant after the star 
crosses, while a few will always set down the instant 
before that event. Any difference between the abso- 
lute and observed times is termed personal equation ; 
and the value of it is susceptible of exact ascertain- 
ment in several ways. The best observer is not one 
whose personal equation is least, but the one whose 



Telescopes and Houses for Them 371 



equation remains most nearly constant. Avoidance 
of the effect of personal equation is practically at- 
tained by the photo-chronograph, an instrument de- 
vised by Father Fargis of Georgetown College for 
recording transits photographically. The telescope is 
set upon the star as if for an ordinary visual observa- 
tion \ but the eye-piece is removed and a tiny sensi- 
tive plate inserted in its stead. In front of it is a 
little strip of metal, or occulting bar, upon which the 
star's image trails in crossing the field ; and this bar 
is connected with an armature, a circuit through which 
is sent by the clock at the beginning of every second, 
as for the ordinary chronograph. This throws the 
bar aside for an instant, so that the developed plate 
shows a succession of black dots, or instantaneous 
and equidistant impressions of 
the star. Holding a lantern for 
a few seconds in front of the 
objective will impress the transit 
lines upon the plate, in their 
correct relation to the stellar 
dots ; and the fraction of a sec- 
ond when the star was crossing 
a wire can then be found by 
measurement, practically free 
from personal equation. 

The first astronomer who dis- 
cussed the inherent and unavoid- 
able deficiencies of instruments and their effects upon 
observations was the versatile von Zach, in his Corre- 
spondance Astronomique in 18 19. In our day a de- 
termination of the errors of an instrument gives vastly 
more trouble than the subsequent observations and the 
reduction or calculation of them. In the almucantar 




THE ALMUCANTAR 
{Devised by Chandler) 



37^ 



Stars and Telescopes 



as used by D T Chandler, many of the troublesome 
errors of the meridian circle are skilfully eluded. The 
flotage principle is adopted for the supports of the 
telescope ; and while the small errors of the meridian 
circle must be found from observations on less than 
half its circle of reference, the almucantar has the 
great advantage of permanent visibility of its entire 
circle of reference, which is the small circle parallel 
to the horizon and passing through the north pole of 
the heavens, often called an almucantar. 



So perfect is the construction of the marine chro- 
nometer at the present day that all observatories now 

use this convenient in- 
strument in recording 
and carrying on the time. 
Its portability, and ease 
of regulation to a rate 
nearly invariable with 
changes of temperature, 
enforce its use on expe- 
ditions where astronomi- 
cal clocks would be im- 
practicable. The chro- 
nometer has received but 
few cardinal modifica- 
tions of design since the 
days of John Harrison, 
who early in the 18th 
century began his great invention, in competition for 
a prize of $100,000 offered by the British government 
in 1 714, for the ' discovery of a method of finding the 
longitude at sea within 30 miles. ' Harrison's chro- 
nometer was taken twice to Jamaica, and on other 




HARRISON (1693-1776) 



Telescopes and Houses for Them 373 

voyages, actually finding the longitude with a precision 
even greater than the margin stipulated, and in 1765 
he was paid the reward, — but only half of it, because 
the prize was divided between him and the brilliant 
Tobias Mayer, of Gottingen, another competitor, who 
had succeeded in bringing the lunar tables to such a 
state of perfection that the longitude of a ship could 




MAYER (1723-I762) 

be found from observations of the Moon as accurately 
as by the chronometric method. Mayer invented 
also the principle of the repeating circle, for eliminat- 
ing the effect of errors of division by repeating the 
measure of an angle on different parts of the graduated 
circle. Harrison's chronometer was in the latter 
part of the century improved by both Arnold and 
Earnshaw \ and is to-day essentially in the form in 
which they left it. It is not our purpose here to enter 



374 



Stars and Telescopes 



upon an explanation of the method of using the chro- 
nometer at sea. That will be found exemplified to the 

fullest detail in the Am- 
erican Practical Navi- 
gator of Nathaniel Bow- 
ditch, whose fame rests- 
also upon his admirable 
translation of the Meca- 
nique Celeste of La Place 
(page 246), which he 
supplemented by useful 
annotations. It is suffi- 
cient to remark here that. 
the chronometer simply 
carries Greenwich time ; 
the difference between 
which and the ship's local 
time gives the longitude. 




bowditch ( 1 773-1838) 



The observatories amply illustrated in the preced- 
ing chapters embody many excellent features, also 
some constructive faults. Astronomers a half century 
and more in the past were accustomed to build their 
observatories high up from the ground, a construction 
far from desirable and always to be avoided if pos- 
sible. Better is it to choose an original site as elevated 
as convenient, and then build the observatory upon it 
only a single story high. Architectural effect must 
often be sacrificed to scientific utility. An attempt to 
combine both met with some measure of success in 
the instructional observatory on the following page, 
built from the writer's specifications in 1886. The 
instruments possess great stability, and all practical 
observers appreciate the absence of long stairways 



Telescopes and Houses for Them 375 

"between dome and transit room. A better form of 
dome wall is shown in D r Roberts's observatory (page 
290), the corners of the square dome-room affording 
a welcome convenience for observing-chairs and other 
accessories. This is the form adopted at Cambridge 
(page 300), which exemplifies the proper construc- 
tion of a great observatory, in marked contrast to the 
main building of the Naval Observatory at Washing- 




*mmh* 



SMITH COLLEGE OBSERVATORY, NORTHAMPTON 
{Miss Mary E. Byrd, Director) 



ton (page 101). Telescopes mounted in individual 
domes, surrounded by low trees and heavy turf, meet 
with minimum interference from the radiating heat 
of early evening. A quiet atmosphere must be se- 
cured at any sacrifice. Massive walls of brick and 
stone are far from conducing to this end ; and the 
observer whose instrument is mounted therein must 
frequently wait several hours for them to cool down 
before beginning his work on summer evenings. The 
best type of observatory construction is that which 
utilizes a minimum of material, so that very little 



376 



Stars and Telescopes 



solar heat can be stored in its walls during the day. 
Local disturbance of the air in early evening is then 
but slight. Louvers, as employed by D r Gill in his 
heliometer house at the Cape, or better still, ivy- 
grown walls, as in the observatory at Oxford University, 
shown below, contribute effectively to this desirable 
end. 

Often circumstances enforce the building of an ob- 
servatory surmounting a dwelling house, or a large 




OXFORD UNIVERSITY OBSERVATORY 
{Professor H. H. Turner, Director) 



school building. M r Brenner's observatory oppo- 
site is an example of this construction ; and the 
observatories built on top of the new high schools at 
Springfield and Northampton, Massachusetts, accord- 
ing to plans furnished by the writer, show the best 
that can be done under restricted conditions. It is 
often difficult to get a telescope so mounted to per- 
form its best : violent tremors of whatever sort, com- 
municated directly to it, are fatal to delicate observa- 



Telescopes and Houses for Them 377 

tion. Also high winds are very unfavorable ; and the 
effect of warmer air from the building below, not to 




MANORA OBSERVATORY, LUSSINPICOLO, ISTRIA 
(M> % Leo Brenner, Director) 

say from adjacent chimneys, is often troublesome. 
This is best avoided by entering the dome, not by a. 
stairway from underneath, but 
from an exterior gallery in the 
open air, usually easy to arrange, 
if specified in due season. But 
if the telescope is small, a port- 
able mounting carried out and 
in as required, and used upon 
a firm foundation, will usually 
yield the most satisfactory vis- 
ion, and at very little expense 
or inconvenience. At the end 
of this chapter will be found a 
list of manuals for the use and 




3-INCH PORTABLE TELESCOPE 

( With altazimuth mounting). 



378 



Stars and Telescopes 



care of such instruments. The earliest and most suc- 
cessful of these is by the Rev. T. W. Webb, late Pre- 
bendary of Hereford Cathedral, and entitled Celestial 
Objects for Common Telescopes, which in 1893 passed 
to a fifth edition under the able revision of the Rev. 
M r Espin. Its closely stocked pages comprise a handy 
book for the practical observer which few professional 
astronomers can afford to despise. 




THOMAS WILLIAM WEBB (1807-1885) 



No less important than optical perfection of a tele- 
scope is excellence of the site where it is to be located 
and used. The greater freedom from cloud the bet- 
ter ; the horizon should be unobstructed, especially to 
the south and west ; and gravel foundations for the 
instruments are worth seeking for. But in addition to 



Telescopes and Houses for Them 379 

all this, optical quietude and transparency of the at- 
mosphere is of the utmost significance. That a per- 
fect telescope may perform perfectly, it must be located 
in a perfect atmosphere. Currents of warm air are 
continually rising from the earth, and colder air is 
coming down to take its place. By removing the 
eye-piece of the telescope these atmospheric waves 
become plainly visible ; and when examining a star 
or planet, their effect appears as blurring, distortion 
or quivering of the image as seen through these shifting 
air strata of variant temperatures and consequently 
variant densities. At M r Lowell's observatory in 
Arizona, his careful assistants have made a thor- 
ough study of these atmospheric waves, and their 
influence upon the conditions of telescopic vision. 
If the air is much disturbed, only the lower magni- 
fying powers can be used, and much of the expected 
.advantage of a great telescope is unavailable. 

All hindrances of atmosphere are found best 
avoided in arid regions of our globe, at elevations 
of 3,000 to 10,000 feet above sea level. A dry 
atmosphere is a prime essential for steady vision. On 
the American continent several observatories are now 
maintained at mountain elevation : the Boyden Ob- 
servatory, Arequipa, Peru (page 382), at 8,000 
feet ; the Lowell Observatory, Flagstaff, Arizona, at 
7,000 feet ; and the Lick Observatory, Mount Ham- 
ilton, California (page 122), at 4.000 feet. Higher 
mountains have as yet been but partially investigated, 
the personal infelicities of occupying them seeming to 
counterbalance the gain afforded by greater elevation. 
But it is an easy assertion that the great telescope of 
the future, if it is to do the work for which it is best 
adapted, must be located at a mountain elevation of 



38o 



Stars and Telescopes 



10,000 to 15,000 feet, in a region where steadiness- 
of atmosphere has previously been assured by critical 
and protracted exploration with that sole condition in 
view. Whether on the lofty table-lands of Asia, or 
those of South America, is yet undecided. 

Of the three greatest benefactors of American 
astronomy, now deceased, two bequeathed their for- 
tune largely to provide 
for great telescopes 
at mountain elevation. 
Both scientific trusts* 
have been so adminis- 
tered as to assure very 
great scientific good. 
James Lick, in 1874, 
by a deed of trust, left 
the sum of about 
§700,000 for the build- 
ing of a telescope more 
powerful than any then 
in existence, and for 
equipping and main- 
taining an observatory 
in conjunction with it. 
Fourteen years were 
consumed in preliminaries, and in building the obser- 
vatory, completing and installing the instruments. 
The subsequent history of the Lick Observatory is 
more widely known than that of any other scientific 
institution in the world. Could M r Lick have known 
the advantages to science and the general diffusion of 
astronomical knowledge accruing from this bequest, 
he would probably have endowed this single object. 
with his entire estate, exceeding §4,000,000. 




JAMES LICK ( 1 796-1876) 



Telescopes and Houses for Them 381 

Uriah A. Boyden, who acquired a snug fortune of 
about 3230,000 from his inventions and improvements 
in turbine water-wheels, bequeathed it all to three 
trustees to ' establish and maintain, in conjunction 
with others, an astronomical observatory on some 
mountain peak.' Harvard College Observatory hav- 
ing received an unrestricted bequest of §100,000 from 
Robert Treat Paine, the two were consolidated in 




URIAH ATHERTOX BOYDEN (1804-1879) 



1886, and the search for a suitable peak began. In 
our own country, lofty elevations in Colorado and 
California w r ere investigated, with unsatisfactory con- 
clusions, after which the field of search was trans- 
ferred to South America. The Chilean desert of Ata- 
cama w r as tested, and later a temporary station was 







w 
o 
w 
ij 
1-1 
o 
u 



Pi 

K 
o 

o 

< 
> 






Telescopes and Houses for Them 383 

established at Chosica in Peru, followed by the per- 
manent observatory now maintained at Arequipa in 
the same country. Two photographic telescopes are 
constantly in use at this remote station, and a pow- 
erful refractor could advantageously be added to the 
working equipment. 

A third great benefactor of astronomy died in 
New Haven in 1889 — Elias Loomis, whose fortune, 











• 


Wa^^m] Wmxm-'- 







ELIAS LOOMIS (181I-1889) 



exceeding §300,000, he left to Yale Observatory, 
reserving its income exclusively for the employment of 
astronomers who should make observations and calcu- 
late them, and for their subsequent publication. 
Professor Loomis was widely known, not only as a 
lecturer and teacher at Yale, but as a writer of highly 



384 Stars and Telescopes 

successful text-books on mathematics and astronomy. 
Also he was a keen investigator in meteorology and 
terrestrial physics, his magnetic charts of the United 
.States being the first published. 

Most of the great telescopes of the world have in 
their turn signalized their extraordinary power by some 
important astronomical discovery — or at least some 
significant piece of research which could not have 
been done so well with a lesser instrument. To 
specify in part : Herschel's reflector first revealed 
the planet Uranus; Lord Rosse's ' Leviathan/ the 
spiral nebulae; the 15 -inch Cambridge telescope, 
Saturn's dusky ring; the 18^-inch Chicago refractor, 
the companion of Sirius ; the Washington 26-inch 
refractor the satellites of Mars ; the 30-inch Russian 
objective, the nebulosities of the Pleiades; and, last 
of all, the 36-inch Lick telescope brought to light a 
fifth satellite of Jupiter. At the time of these dis- 
coveries, each of the great telescopes was almost the 
only instrument powerful enough to have made the 
discovery. With such a record, are we not safe in 
predicting further advances with larger telescopes still ? 
Two American opticians of wide experience and high 
competency stand ready to undertake them, if only the 
funds are forthcoming ; and as yet there is no indication 
that a refracting telescope of five, or even six, feet aper- 
ture would fail of a gratifying success to its projector. 

According to Alvan Graham Clark, a six-foot 
objective would not necessitate a combined thickness 
of more than six inches ; and he also says, ' Who 
knows how soon glass still more transparent may be 
at hand, considering the steady improvement made in 
this line, and the fact that the present disks are infi- 
nitely superior to the early ones?' The obstacles to 



Telescopes and Houses for Them 385 



overcome in mounting and using such a glass dis- 
appear when we reflect that as yet the astronomer 
has but just begun to invoke the fertile resources of 
the modern engineer. The younger Clark further 
wrote, in 1893, this remarkable union of fact and 
prophecy: 'The increase in size of even our present 
great refractors is not a possibility but a fact, and 
with this will come large acquisitions to our present 
stock of knowledge. The new astronomy, as well as 
the old, demands more power. Problems wait for 
their solution, and theories to be substantiated or dis- 
proved. The horizon of science has been greatly 
broadened within the last few years, but out upon the 
border-land I see the glimmer of new lights that wait 
for their interpretation, and the great telescopes of 
the future must be their interpreters.' 



EX-LIBRJS 




JOHANNIS COVCH ADAMS 



386 Stars and Telescopes 



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P- x 95- 
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Brita?mica, vol. xxi. (i860), 117. 
Wolf, R., Geschichte der Astro momie (Munich 1877). 
Poggendorff, Geschichte der Physik (Leipzig 1S79). 
Knight, E. H., ' Telescope/ American Mechanical Dictionary r 

vol. iii. (Boston 18S1). 
Pickering, 'Large Telescopes/ Proc. Am. Acad. Arts and Sci- 

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Blrnham, Denning, Young, ' Small vs. Large Telescopes/ 

Sid. Mess.iv. (1885), 193, 259; v. (18S6), 1. 
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Knight, W. H., ' Telescopes in the U. S./ The Sidereal Mes- 
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Vogel, Newcomb-Engelmann's Popular e Astronomie (Leip- 
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Clark, ' Possibilities of the Telescope/ North American Re- 
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Clark, ' Future Great Telescopes/ Astrono7?iy and Astro- 
physics, xii. (1893), 67 3- 

Warner, ' Engineering Problems of Large Refractors/ As- 
tronomy and Astrophysics, xii. (1893), ^95- 



Telescopes and Houses for Them 387 

Grubb, H., ' Great Telescopes/ Knowledge, xvii. (1894), 9S. 
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Xkwcomb, ' Telescopes/ Johnson's Univ. Cycl. viii. (1895). 
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(Breslau 1895-9S). 
Barnard, ' Large and Small Telescopes/ M. N. Roy. Astron. 

Soc. lvi. (1S96), 163. 
Hale, ' Yerkes Telescope/ Astrophys. Jour. vi. (1897), 37. 
Lewis, Hollis, ' Large Refractors/ The Observatory, xxi. 

(1S9S), 239, 270. 
Fowler, ' Concise Knowledge Library/ Astronomy, part ii. 

(New York 1S9S). 

Glass, Objectives, and Testing 

Rutherfurd, ' Spectroscope in Testing Objective/ Am. Jour. 

Set. lxxxix. (1865), 307. 
Gundlach, ' Quadruple Objectives/ Astr. iVachr. xci. (1878), 

177- 

Hastings, ' Achromatic Objective//". H. Univ. Circ. ii. (1882), 

Xo. 19. 
Smith, H. L., ' Short-focus/ Sidereal Messenger, i. (1883), 2 39« 
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Hastings, 'Figuring Lenses/ Sidereal Messe7iger, i. 244; ii» 

39(iSS 3 -S 4 ). 
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Grubb, H., ■ Objectives and Mirrors : Preparation and Test- 
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Young, 'Lick Objective/ Boston Jour. Chem. (October 1S86). 
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Conroy, 'Reflection and Transmission of Light by Glass/ 

Phil. Trans, clxxx. (1889), 245. 
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160. 
Cooke, On the Adjustment and Testing of Telescopic Objectives y 

(York 1S91). 
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219. 
Taylor, ' New Achromatic Objective,' M. N. Roy. Astron. Soc. 

liv. (1S94), 32S. 



388 Stars and Telescopes 

Brashear, 'Optical Glass/ Pop. Astron. i. (1894), 221, 241, 

291, 447. 
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ii. (1894), 9, 57- 
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104. 

Reflectors and their Mountings 

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(1869), 127. 
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(London 1877). 
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xlvi. (1881), 173. 
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liii. (1893), I 9- 
"Clerke, The Herschels and Modern Astronomy (London 1895). 
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Schaeberle, ' Cassegrain/ Ptcb. Ast. Soc. Pacific, vii. (1895), 

185. 

Stoney, ' Supporting Large Specula/ M. N. Roy. Astron. Soc. 

lvi. (1896), 454. 
Hale, ' Reflectors vs. Refractors/ Astrophysical Journal, v. 

(1897), 119. 
Wadsworth, ' Coude Reflectors/ Astrophysical Journal, v. 

(1897), 132. 
Gautier, ' Siderostat a lunette de 6o m de foyer et i m .25 d'ou- 

verture/ Annuaire Bur. Long. 1899. 






Telescopes and Houses for Them 389 



Spectroscopy and Spectroscopes 

Schuster, ' Modern Spectroscopy/ Proc. Roy. Inst. ix. (1881), 

493-' 

Lockyer, * Spectroscopic Apparatus and Methods,' The Chem- 
istry of the Sun (London and X. Y. 1887). 

Maunder, in Chambers's Descriptive Astronomy, ii. (Oxford 
1890). 

Keeler, 'Elementary Principles of Spectroscopes,' The Sid- 
ereal Messenger, x. (1891), 433. 

Deslandres, Comptes Rendtts, cxiii. (1891), 308; cxiv. (1892), 
276. 

Frost, ' Potsdam Spectrograph,' Astronomy and Astro-Physics, 
xii. (1893), 150. 

Hale, ' Spectroheliograph,' Astronomy and Astro-Physics, xii. 
(1893), 241. 

Keeler, ' Spectroscope/ Pop. Astron. i., ii. (1893-94). 

Frost, Scheiner, Treatise o?i Astronomical Spectroscopy (Bos- 
ton and London 1894). Bibliography. 

Reed, ' Spectroscope/ Pop. Astron. ii. (1895). 

Young, ' Spectroscope and Adjustments/ The Sun, p. 351 
(Xew York 1896) ; Pop. Astron. v. (1897), 318. 

Wadsworth, ' Resolving Power,' Astro. Jour. vi. (1897), 27. 

Michelson, 'Echelon Spectroscope/ Astrophys. Jour. viii. 
(1898), 37. 

Campbell, 'New Spectrograph/ Astrophys. Jour. viii. (1898), 
123. 

Poor, ' Concave Grating/ M. N. Roy. Astron. Soc. lviii. (1898), 
291. 

The books and papers on celestial spectroscopy are exhaus- 
tively cited in D r Alfred Tuckermax's ' Index to the Liter- 
ature of the Spectroscope/ Smithsonian Miscellaneous Collections, 

No. 658 (1888), pp. 8, 66. 

General Treatises, Special Instruments, and New 
Methods 

Hansen, Die Theorie des Aequatoreals (Leipzig 1855). 

Shadwell, Management of Chrono??ieters (London 1861). 

Karl, Principien der AstronomischeJi Instrumentenkunde (Leip- 
zig 1863). 1 

Xewcomb, ' Theory of Meridian Circle/ Washington Observa- 
tions 1865, Appendix i. 



390 Stars and Telescopes 

Kaiser, 'Double-image Micrometer,' Leyde7i Obs. iii. (1872). 
Davis, C. H., ' Ratings of Chronometers/ Washington Observa- 
tions 1875, App. iii. 
Gill, ' Heliometer/ Dun Echt Obs. Publications, ii. (1877). 
Seeliger, Theorie des Heliometers (Leipzig 1877). 
Lockyer, Stargazing: Past and Prese7it (London 1878). 
Godfray, A Treatise on Astro7iomy (London 1880). 
Todd, ' Orbit-sweeper/ Proc. A7n. Acad. xv. (1880), 270. 
Harkness, ' Flexure of Meridian Instruments/ Wash. Obs. 

1882, App. iii. 
Clark, L., Treatise 071 the Tra7isit I7ist)-U7ne7it (London 1882). 
V. KoNKOLY, Praktische A7ileitii7ig zur A7istellung Astron. 

Beobachtii7ige7i (Brunswick 1883). 
Harrington, ' Tools of the Astronomer/ Sidereal Messenger, 

ii. (1883-84). 
Brashear, 'Optical Surfaces/ Proc. Am. Assoc. Adv. Sci. 

xxxiii. (1884), 255. 
Loewy, 'Equatorial Coude/ Bulletin Asiro7i. i. (1884), 265. 
Radau, ' Heliostats/ Bulleti7i Astron. i. (1884), 153. 
Newcomb, Rece7it l77iprove77ie7its in Astro7i. I7istru7ne7its (Wash- 
ington 1884). 
Hough, ' Printing Chronograph/ Sidereal Mess. v. (1886), 161. 
Chandler, ' Almucantar/ A/mals Harv. Coll. Obs. xvii. (1887)* 
Grubb, H., ' Electric Control/ M. N. R. A. S. xlviii. (1888), 352. 
Chandler, ' Square Bar Micrometer/ Mem. A771. Acad. xi. 

(1888), 158. 
Langley, Young, Pickering, ' Wedge Photometer/ Mem. 

Am. Acad. xi. (1888), 301. 
Sanford, ' Personal Equation/ Am. Jour. Psychology, ii. (1889), 

3, 271, 403. Bibliography. 
Michelson, 'Interference Methods/ Phil. Mag. xxx.(i89o), 1. 
Rogers, J. A., ' Correction of Sextants/ S7nithso7iian Misc. Coll. 

No. 764 (1890). 
Hagen, The Photochronograph (Georgetown Coll. Obs. 1891). 
Clerke, ' Instruments and Methods/ Hist, of Ast7-07i. during 

XIX Ce7itury (London 1893). 
Huggins, M. L., ' Astrolabe,' Pop. Astron. ii. (1895), J 99- 
Becker, E., Herz, ' Micrometer, Personal Equation, Transit 

Instrument/ Valentiner's Ha7idwbrterbuch der Aslro7iomie 

(Breslau 1895-98). 
Stoney, ' Siderostat/ M. JV. P. Ast. Soc. lvi. (1896), 456. 
Hamy, 'Temperature Effect/ Bull. Astr. xiii. (1896), 178. 
Turner, 'Ccelostat/ M. N. R. A. S. lvi. (1896), 408. 



Telescopes and Houses for Them 391 

Muller, Die Photometrie der Gestirne (Leipzig 1897). Bibli- 
ography. 
Updegraff, ' Flexure,' Trans. Acad. Sci. St Louis ni. (1897), 

No. 11. 
Todd, A New Astronomy, Chapter ix. (New York 1897). 
Lippmann, 'Coelostat/ Bulletin Astronomique, xiv. (1897), 369. 
The literature of astronomical instruments by the able writers 
of the Encydopcedia Britannica is summarized in Baldwin's 
Syste?natic Readings in E. B., p. 94 (Chicago and New York), 
1897. Many novel devices of service to astronomer and astro- 
physicist are described and figured in the Berlin monthly begun 
in 1 88 1, entitled Zeitschrift ficr Instrumentenkunde. 



Observatories 

Struve, F. G. W., Description de V Observatoire de Poulkova (St 

Petersburg 1845). 
Main, Encycl. Brit. 8th ed. iii. (1853), 8l6 - 
Loomis, Recent Progress of Astronomy, especially in U. S. (New 

York 1856). 
Andre, Rayet, An got, L } Astrono?nie Pratique et les Obser- 

vatoires en Europe et en Amerique (Paris 1874-78). 
Perrotin, Visite a~ divers Observatoires d' Europe (Paris 188 1). 
Newcomb, No. Am. Rev. exxxiii. (1881), 196; Nature, xxvi. 

(1882), 326. 
Dreyer, ' Observatories/ Encycl. Brit., 9 ed. xvii. (1884), 708. 
Perrotin, Annates de ? Observatoire de Nice, i. (Paris 1885). 
Winterhalter, * European Observatories/ Washiiigton Obs. 

1885, App. i. 
Todd, ' Observatories in America,' Nation, xlvii. (1888), 25. 
Young, ' European Observatories,' Scribner's Magazine, iv. 

(1888), 82. 
Love, 'First College Obs. in U. S.,' Sid. Mess. vii. (1888), 417. 
Clerke, 'Cape Observatory/ Contemp. Review, lv. (1889), 380. 
Lancaster, Liste Generate des Observatoires, etc. (Brussels 1890). 
Chambers, Descriptive and Practical Astroiiomy (Oxford 1890). 
Swift, 'New Observatories/ Appleton's Annual Cyclopcedias 

(1890-98). 
Gill, ' Work in Modern Observatory/ Proc. Royal Inst. xiii. 

(1891), 402. 
Upton, ' Ancient and Modern Observatories/ The Sidereal 

Messenger, x. (1891), 481. 



39 2 Stars and Telescopes 

Proctor, Ranyard, Old and New Astronomy (London and 

New York 1892). 
Algue, ' Observatory at Manila/ Astron. and Astro-Phys. xiii. 

(1894), 85. 
Payne, ' Free Public Observatories,' Astron. a?id Astro-Phys. 

xiii. (1894), no. 
Lynn, ' Observatories a Century Ago/ Knowledge, xviii. (1895), 

86. 
Newcomb, ' Observatories/ Johnson's Univ. Cycl. vi. (1895). 
Valentiner's Handworterbuch der Astronomie (Breslau 1895 

-1899). 
Stoney, Wadsworth, ' Astrophysical Observatory/ Astrophys. 

Jour. iv. (1896), 238. 
Janssen, 'Annates de P Observatoi?-e a" Astronomie Physique, i. 

(Paris 1896). 
Jacoby, 'Cape Observatory/ Pop. Astron. iii. (1896), 217. 
Stoney, ' Future Astrophys. Observatory/ M. N. Roy. Astron. 

Soc. lvi. (1896), 452. 
Hale, ' Yerkes Observatory/ Astrophys. Jour, v., vi. (1897). 
Hale, ' Aim of the Yerkes Observatory/ Astrophys. Jour. vi. 

(1897), 310. 
Payne, 'Yerkes Observatory/ Pop. Astron. v. (1897), 115. 
Newcomb, ' Aspects of American Astronomy/ Pop. Astron. v. 

(1897), 351. 
Meyers Konversatioiis-Lexikon, Bd. xvi., p. 418 (Leipzig and 

Vienna 1897). 
Witt, * Meudon Observatory/ Himmel und Erde, x. (1898), 

5 2 9. 
Colin, ' End of Tananarivo Observatory/ The Observatory, 

xxi. (1898), 305. 
Meyer, Das Weltgebaude (Leipzig and Vienna 1898). 

For detailed descriptions of observatories, and instruments 
and the work done with them, consult the volumes of their 
annals, especially Pulkowa, Greenwich, Paris, Washington, 
Cambridge (U. S.), Nice, Mount Hamilton (Lick), Dunsink, 
and Leyden. For reports of observatories, refer to the Monthly 
Notices Royal Astronomical Society for February each year, and 
to the Vierteljahrsschrift der Astronomischeit Gesellschajt, pub- 
lished at Leipzig. The publications of observatories of all 
countries are excellently summarized by D r Copeland, in the 
elaborate Catalogue of the Crawford Library of the Royal 
Observatory, pp. 325-45 (Edinburgh 1890). 



Telescopes and Houses for Them 393 



Celestial Photography 

Bond, G. P., ■ Stellar Photography/ Astron. Nachrichten, xlviu 

(1S58); xlviii. (1858); xlix. (1859). 
De la Rue, ■ Celestial Photography in England/ Report BriL. 

Assoc. Adv. Sci. 1859, p. 130. 
Draper, ' Reflector for Photography/ Smithson. Contr. KnowU 

xiv. (1S65). 
Rutherfurd, * Astr. Photography/ Am. Jour. Sci. lxxxix. 

(1S65), 304. 
Newcomb, * Photography of Precision/ Papers U. S. Transit: 

of Venus Commission, i. (Washington 1872). 
Harkness, * Photoheliograph/ Memoirs Roy. Astr. Soc. xliii... 

(1877), 129. 
Gould, ' Celestial Photography/ The Observatory, \\. (1879), 13. 
Pritchard, ' Photography of Precision/ Mem. Roy. Astr. Soc* 

xlvii. (1883), I. 
Common, ' Telescopes for Astr. Photog./ Nature, xxxi. (1884-5), 

38, 270. 
Common, ' Photography as Aid to Astronomy/ Proc. Roy. In- 

stitution, xi. (1885), 367. 
Winterhalter, ' Astrophotographic Congress/ Washington 

Obs. (1885, App. i.). 
Henry, 'Astr. Photography/ Nature, xxxiv. (1886), 35. 
Struve, O., f Die Photographie im Dienste der Astronomie/ 

Bull. Acad. Sci. St Petersbourg, xxx. (1886), N r 4. 
Rayet, 'History/ Bulletin Astronomique, iv. (1887), 165. 
Common, ' Astron. Photography/ Nineteenth Century, xxk 

(1887), 227. 
Mouchez, ' Astrographic Survey/ Annuaire Bur. Long. 1887. 
Mouchez, La Photographie Astronomique (Paris 1887). 
Gill, ' Applications of Photography in Astronomy/ Proc. Royal 

Institution, xii. (1887), 158. 
V. Konkoly, Praktische Anleitung zur Himmelsphotographie 

(Halle 1887). 
, ■ Astr. Photography/ Sid. Mess. vii. (1888), 138, 181 ;. 

Edinburgh Review, clxvii. (1888), 23. 
Pickering, E. C, ' Stellar Photography/ Mem. Am. Acad. xi. 

(1888), 179. 
Chambers, 'Astron. Photography/ Descriptive Astronomy, ii.. 

(Oxford 1890). 
Schooling, Westminster Review, exxxvi. (1891), 303. 
Russell, The Star Camera (Sydney 1891). 



394 Stars and Telescopes 

Brothers, Photography : its History, Processes, Apparatus, and 

Materials (London 1892). 
Fraissinet, ' Paris Astrographic Observatory/ La Nature, 

1893. 
Taylor, ' Photographic Objectives/ M. N. Roy. Astron. Soc. 

liii. (1893), 359. 
Turner, Lewis, ' Astrographic Chart/ The Observatory, xvi. 

(1893), 4°7 5 Astron. and Astro-phys. xiii. (1894), 20. 
Roberts, ' Progress in Photography/ Proc. Am. Phil. Soc. 

xxxii. (1894), 97. 
Russell, ' Progress/ Pop. Astron. ii. (1894-95). 
Pickering, W. H., 'Astr. Photog./ Ann. Harv. Coll. Obs. 

xxxii. (1895). 
Barnard, ' Astronomical Photography/ The Photographic 

Times, xxvii. (1895), 65. 
Roberts, ' Reflector and Portrait Lens/ Jour. Brit. Astr. Assoc. 

vi. (1896), 332. 
Gill, Kapteyn, ' Stellar Photography/ Annals Cape Observa- 
tory, iii. (London 1896). 
Schaeberle, ' Planetary Photography/ Pop. Astron. iii. (1896), 

280, 
Turner, ' Photo. Transit Circle/ M. N. Roy. Astron. Soc. lvii. 

(1897), 349- 
Wadsworth, ' Planetary Photography/ The Observatory, xx. 

(1897). 
Pickering, E. C, ' Bruce Photographic Telescope/ Pop. Astron. 

iv. (1897), 531. 
Deslandres, Specimens de Photographies Astronomiqices (Paris 

1897). 
Scheiner, Die Photographie der Gestirne (Leipzig 1897). Bib- 
liography. 
Loewy, Puiseux, ' Lunar Photography/ Annuaire Bur. Long, 

1898, A. 
Schweiger-Lerchenfeld, Atlas der Himmelskunde (Vienna 

1898). 
Barnard, 'Development of Photography/ Proc. Am. Assoc. 

Adv. Science, xlvii. (Salem 1898) ; Pop. Ast. vi. (1898), 425. 

In Houzeau's Vade-Mecu7n de V Astronome, p. 339 (Brussels 
1882), the earlier scientific papers on astronomical photography 
are catalogued. All the preceding bibliographies need to be 
supplemented by the classified lists of The Astrophysical Jour- 
nal, i.-ix. (1895-99). 



Telescopes and Houses for Them 395 



Mountain Observatories 

Smyth, C. P., 'Teneriffe/ Phil. Trans. Roy.Soc. cxlviii. (1858), 

465. 
Smyth, C. P., Teneriffe, an Astronomer's Experiment (London 

1858). 
LANGLEY, ' Aetna/ Am. Jour. Science, xvii. (1879), 259; xx. 

(1880), 33. 
Langley, ' Mount Whitney Expedition/ Nature, xxvi. (1882), 

314. 
Pickering, 'Mountain Observatories/ Sid. Mess. ii. (1883), 105. 
Copeland, 'Experiments in the Andes/ Copernicus, iii. (1884), 

193- 
, ' Mountain Observatories/ Edinburgh Review, clx. 

(1884), 351 ; Pop. Sci. Monthly, xxvi. (1885), 388. 

Todd, 'Lick Observatory/ Science, vi. (1885), 181, 186. 

H olden, Handbook of the Lick Observatory (San Francisco 
1888). 

Ranyard, Knowledge, xii. (1889), 125. 

Janssen. ' Mt. Blanc Observatory/ Annuaire Bur. Long. (1894- 
1899). Also Rept. Smithsonian Lnstitution 1894, p. 237. 

Holden, ' Mountain Observatories/ Smithsonian Misc. Col- 
lections, 1035 (1896). Bibliography. 

Douglass, ' Atmosphere, Telescope, and Observer/ Pop. Ast 
v. (1897), 64. 

See, 'Air Waves and Currents/ Popular Astron. v. (1898), 479. 

See, ' Mountain Observatories/ Popular Astron. vi. (1898), 65. 

Douglass, ' Scales of Seeing/ Popular Astron. vi. (1898), 193. 

Popular literature of the telescope, celestial photography, and 
the spectroscope has experienced an enormous growth, par- 
ticularly in recent years. A nearly complete bibliography of 
titles may be found on reference to Poole's Lndexes, at the 
pages given below ; supplemented, of course, by the annual 
volumes for 1897, 1898 : — 



Volume of Index 


Observatories 


Photography 


Spectroscopes 


Telescopes 


I. (1800-81) 
II. (1882-86) 

III. (1887-91) 

IV. (1892-96) 


P. 936 

3*9 
3°9 
410 


p. 1003 

340 

33° 
440 


P- 1233 
413 
403 
540 


p. I29I 

433 
423 
567 



396 Stars and Telescopes 



Practical Astronomy and Making Observations 

Pearson, Introduction to Practical Astronomy (London 1824- 

29). With Appendix and Plates. 
•Mason, Introduction to Practical Astronomy (New York 1841). 
Loo Mis, Introductio7i to Practical Astronomy (New York 1855), 
Chauvenet, Manual of Spherical and Practical Astrononiy 

(Philadelphia 1863). 
Proctor, Half-hours with the Telescope (New York 1873). 
Sawitsch, Peters, A briss der Praktischen Astronomie (Leipzig 

1879). 
Smyth, Chambers, A Cycle of Celestial Objects (Oxford 1881). 
Souchon, Traite d' Astronomic Pratique (Paris 1883). 
Doolittle, Treatise on Practical Astronomy as applied to 

Geodesy and Navigation (New York 1885). 
Noble, Hoitrs with a Three-inch Telescope (New York 1887). 
Serviss, Astro7iomy with an Opera Glass (New York 1888). 
Oliver, Astronomy for Amateurs (London and New York 1888), 
Denning, Telescopic Work for Starlight Evenings (London, 

1890. 

Campbell, Handbook of Practical Astronomy (Ann Arbor 1891). 
Greene, hitroduction to Spherical and Practical Astronomy 

(Boston 1891). 
Colas, Celestial Handbook (Chicago 1892). 
Webb, Espin, Celestial Objects for Co?m?ion Telescopes (London 

i893~94)- 
Gibson, The Amateur Telescopisfs Handbook (New York 1894).. 
Comstock, * Practical Astronomy/ Bull. Univ. Wisconsin, i. 

(1895), No. 3. 
Fowler, Popular Telescopic Astro?iomy (London 1896). 
Mee, Observational Astronomy (Cardiff and London 1897). 
Brenner, Handbuch fur A??zateur Astronomen (Leipzig 1898). 

Supplementary to the foregoing handbooks are the annual 1 
' Companion' to The Observatory; also the monthly notes in 
Popular Astronomy, and in the Picblications of the Astronomical 
Society of the Pacific, together with ephemerides in the Annuaire 
du Bureau des Longitudes. 



Small Planets between Mars and Jupiter 397 



THE SMALL PLANETS BETWEEN MARS AND JUPITER 



NUM- 




DATE OF 


DISCOVERER AND 


PLACE OF 


BER 




DISCOVERY 


HIS NUMBER 


DISCOVERY 


I 


Ceres 


I Jan. 1801 


Piazzi 


Palermo 


2 


Pallas 


28 Mar. 1802 Olbers , 


Bremen 


3 


Juno 


1 Sept. 1804 


Harding 


Lilienthal 


4 


Vesta 


29 Mar. 1807 


Olbers 2 


Bremen 


5 


Astraea 


8 Dec. 1845 


Hencke i 


Driessen 


6 


Hebe 


1 July 1847 


Hencke 2 


Driessen 


7 


Iris 


13 Aug. 1847 


Hindi 


London 


8 


Flora 


18 Oct. 1847 


Hind 2 


London 


9 


Metis 


25 Apr. 1848 


Graham 


Markree 


10 


Hygeia 


12 Apr. 1849 


De Gasparis 1 


Naples 


11 


Parthenope 


11 May 1850 


De Gasparis 2 


Naples 


12 


Victoria 


13 Sept. 1850 


Hind 3 


London 


13 


Egeria 


2 Nov. 1850 


De Gasparis 3 


Naples 


14 


Irene 


19 May 1851 


Hind 4 


London 


IS 


Eunomia 


29 July 1851 


De Gasparis 4 


Naples 


16 


Psyche 


17 Mar. 1852 


De Gasparis 5 


Naples 


17 


Thetis 


17 Apr. 1852 


Luther x 


Bilk 


18 


Melpomene 


24 June 1852 


Hind 5 


London 


19 


Fortuna 


22 Aug. 1852 


Hind 6 


London 


20 


Mass alia 


19 Sept. 1852 


De Gasparis 6 


Naples 


21 


Lutetia 


15 Nov. 1852 


Goldschmidt x 


Paris 


22 


Calliope 


16 Nov. 1852 


Hind 7 


London 


23 


Thalia 


15 Dec. 1852 


Hind 8 


London 


24 


Themis 


5 Apr. 1853 


De Gasparis 7 


Naples 


25 


Phocaea 


6 Apr. 1853 


Chacornac x 


Marseilles 


26 


Proserpine 


5 May 1853 


Luther 2 


Bilk 


27 


Euterpe 


8 Nov. 1853 


Hind 9 


London 


28 


Bellona 


1 Mar. 1854 


Luther 3 


Bilk 


29 


Amphitrite 


1 Mar. 1854 


Marth 


London 


30 


Urania 


22 July 1854 


Hind 10 


London 


3i 


Euphrosyne 


1 Sept. 1854 


Ferguson 1 


Washington 


3 2 


Pomona 


26 Oct. 1854 


Goldschmidt 2 


Paris 


33 


Polyhymnia 


28 Oct. 1854 


Chacornac 2 


Paris 


34 


Circe 


6 Apr. 1855 


Chacornac 3 


Paris 


35 


Leucothea 


19 Apr. 1855 


Luther 4 


Bilk 



398 



Stars and Telescopes 



NUM- 




DATE OF 


DISCOVERER AND 


PLACE OF 


BER 




DISCOVERY 


HIS NUMBER 


DISCOVERY 


36 


Atalanta 


5 Oct. 185c; 


Goldschmidt 3 


Paris 


37 


Fides 


5 Oct. 1855 


Luther 5 


Bilk 


38 


Leda 


12 Jan. 1856 


Chacornac 4 


Paris 


39 


Laetitia 


8 Feb. 1856 


Chacornac 5 


Paris 


40 


Harmonia 


31 Mar. 1856 


Goldschmidt 4 


Paris 


4i 


Daphne 


22 May 1856 


Goldschmidt 5 


Paris 


42 


Isis 


23 May 1856 


Pogson 1 


Oxford 


43 


Ariadne 


15 Apr. 1857 


Pogson 2 


Oxford 


44 


Nysa 


27 May 1857 


Goldschmidt 6 


Paris 


45 


Eugenia 


27 June 1857 


Goldschmidt 7 


Paris 


46 


Hestia 


16 Aug. 1857 


Pogson 3 


Oxford 


47 


Aglaia 


15 Sept. 1857 


Luther 6 


Bilk 


48 


Doris 


19 Sept. 1857 


Goldschmidt 8 


Paris 


49 


Pales 


19 Sept. 1857 


Goldschmidt 9 


Paris 


5o 


Virginia 


4 Oct. 1S57 


Ferguson 2 


Washington 


51 


Nemausa 


22 Jan. 1858 


Laurent 


Nismes 


52 


Europa 


4 Feb. 1858 


Goldschmidt 10 


Paris 


53 


Calypso 


4 Apr. 1858 


Luther 7 


Bilk 


54 


Alexandra 


10 Sept. 1858 


Goldschmidt n 


Paris 


55 


Pandora 


10 Sept. 1858 


Searle 


Albany 


56 


Melete 


9 Sept. 1857 


Goldschmidt 12 


Paris 


57 


Mnemosyne 


22 Sept. 1859 


Luther 8 


Bilk 


58 


Concordia 


24 Mar. i860 j Luther Q 


Bilk 


59 


Olvmpia 


12 Sept. i860 


Chacornac 6 


Paris 


60 


Echo 


15 Sept. i860 


Ferguson 3 


Washington 


61 


Danae 


9 Sept. i860 


Goldschmidt 18 


Chatillon 


62 


Erato 


14 Sept. i860 


Foerster& Lesser 


Berlin 


63 


Ausonia 


10 Feb. 1861 


De Gasparis 8 


N aples 


64 


Angelina 


4 Mar. 1861 


Tempel x 


Marseilles 


<35 


Maximiliana 


8 Mar. 1861 


Tempel 2 


Marseilles 


66 


Maia 


9 Apr. 1861 


Tuttle ! 


Cambridge, U. S. 


67 


Asia 


17 Apr. 1861 


Pogson 4 


Madras 


68 


Leto 


29 Apr. 1861 


Luther 10 


Bilk 


69 


Hesperia 


29 Apr. 1861 


Schiaparelli 


Milan 


70 


Panopaea 


5 May 1 861 


Goldschmidt 14 


Paris 


71 


Niobe 


13 Aug. 1861 


Luther u 


Bilk 


72 


Feronia 


29 May 1861 


Peters j & Safford 


Clinton 


73 


Clytia 


7 Apr. 1862 


Tuttle 2 


Cambridge, U. S. 


74 


Galatea 


29 Aug. 1862 


Tempel 3 


Marseilles 


75 


Eurydice 


22 Sept. 1862 


Peters 2 


Clinton 



Small Planets between Mars and Jupiter 399 



NUM- 




DATE OF 


DISCOVERER AND 


PLACE OF 


BER 




DISCOVERY 


HIS NUMBER 


DISCOVERY 


76 


Freia 


21 Oct. IS62 


D'Arrest 


Copenhagen 


77 


Frigga 


12 XOY. lS62 


Peters 3 


Clinton 


;s 


Diana 


15 Mar. 1S63 


Luther 12 


Bilk 


79 


Eurynome 


14 Sept 1S63 


Watson 1 


Ann Arbor 


80 


Sappho 


2 May 1864 


Pogson 5 


Madras 


Si 


Terpsichore 


30 Sept. 1864 


Tempel 4 


Marseilles 




Alcmene 


27 Nov. 1864 


Luther 13 


Bilk 


S3 


Beatrix 


26 Apr. 1S65 


De Gasparis 9 


Naples 


84 


Clio 


25 Aug. 1S65 


Luther 14 


Bilk 


S5 


Io 


19 Sept. 1865 


Peters 4 


Clinton 


86 


Semele 


4 Jan. 1866 


Tietjen 


Berlin 


s 7 


Sylvia 


16 May 1866 


Pogson 6 


Madras 


SS 


Thisbe 


15 June 1866 


Peters 5 


Clinton 


S 9 


Julia 


6 Aug. 1S66 


Stephan 


Marseilles 


90 


Antiope 


1 Oct. 1S66 


Luther 15 


Bilk 


9i 


^Egina 


4 Nov. 1S66 


Borrelly i 


Marseilles 


92 


Undina 


7 July 1867 


Peters 6 


Clinton 


93 


Minerva 


24 Aug. 1867 


Watson 


Ann Arbor 


94 


Aurora 


6 Sept. 1867 


Watson 3 


Ann Arbor 


95 


Arethusa 


2^ Nov. 1867 


Luther 16 


Bilk 


96 


iEgle 


17 Feb. 1868 


Coggia j 


Marseilles 


97 


Clotho 


•17 Feb. 1868 


Tempel 5 


Marseilles 


98 


Ianthe 


18 Apr. 1868 


Peters 7 


Clinton 


99 


Dike 


28 May 186S 


Borrelly 2 


Marseilles 


100 


Hecate 


11 July 1868 


Watson 4 


Ann Arbor 


101 


Helena 


15 Aug. 1868 


Watson 5 


Ann Arbor 


102 


Miriam 


22 Aug. 1S68 


Peters 8 


Clinton 


103 


Hera 


7 Sept. 1868 


Watson 6 


Ann Arbor 


104 


Clymene 


13 Sept. 1868 


Watson 7 


Ann Arbor 


105 


Artemis 


16 Sept. 1S68 


Watson 8 


Ann Arbor 


106 


Dione 


10 Oct. 1868 


Watson 9 


Ann Arbor 


107 


Camilla 


17 Nov. 1868 


Pogson 7 


Madras 


10S 


Hecuba 


2 Apr. 1S69 


Luther l7 


Bilk 


109 


Felicitas 


9 Oct. 1869 


Peters 9 


Clinton 


1:0 


Lydia 


19 Apr. 1870 


Borrelly 3 


Marseilles 


in 


Ate 


14 Aug. 1870 


Peters 10 


Clinton 


112 


Iphigenia 


19 Sept. 1S70 


Peters n 


Clinton 


"3 


Amalthea 


12 Mar. 1871 


Luther 18 


Bilk 


114 


Cassandra 


23 July 1S71 


Peters 12 


Clinton 


"5 


Thyra 


6 Aug. 1S71 


Watson 10 


Ann Arbor 



400 



Stars and Telescopes 



NUM- 




DATE OF 


DISCOVERER AND 


PLACE OF 


BER 




DISCOVERY 


HIS NUMBER 


DISCOVERY 


Tl6 


Sirona 


8 Sept. 187 1 


Peters 13 


Clinton 


117 


Lomia 


12 Sept. 1871 


Borrelly 4 


Marseilles 


118 


Peitho 


15 Mar. 1872 


Luther 19 


Bilk 


119 


Althaea 


3 Apr. 1872 


Watson n 


Ann Arbor 


120 


Lachesis 


10 Apr. 1872 


Borrelly 5 


Marseilles 


121 


Hermione 


12 May 1872 


Watson 12 


Ann Arbor 


122 


Gerda 


31 July 1872 


Peters 14 


Clinton 


123 


Brunhilda 


31 July 1872 


Peters 15 


Clinton 


124 


Alceste 


23 Aug. 1872 


Peters 16 


Clinton 


125 


Liberatrix 


11 Sept. 1872 


Pros. Henry x 


Paris 


126 


Velleda 


5 Nov. 1872 


Paul Henry x 


Paris 


127 


Johanna 


5 Nov. 1872 


Pros. Henry 2 


Paris 


128 


Nemesis 


25 Nov. 1872 


Watson 13 


Ann Arbor 


I29 


Antigone 


5 Feb. 1873 


Peters 17 


Clinton 


I30 


Electra 


17 Feb. 1873 


Peters 18 


Clinton 


131 


Vala 


24 May 1873 


Peters 19 


Clinton 


132 


;£thra 


13 June 1873 


Watson 14 


Ann Arbor 


*33 


Cyrene 


16 Aug. 1873 


Watson 15 


Ann Arbor 


134 


Sophrosyne 


27 Sept. 1873 


Luther 20 


Bilk 


*35 


Hertha 


18 Feb. 1874 


Peters 20 


Clinton 


J 36 


Austria 


18 Mar. 1874 


Palisa x 


Pola 


*37 


Meliboea 


21 Apr. 1874 


Palisa 2 


Pola 


138 


Tolosa 


19 May 1874 


Perrotin 1 


Toulouse 


'39 


Juewa 


10 Oct. 1874 


Watson 16 


Pekin 


140 


Siwa 


13 Oct. 1874 


Palisa 3 


Pola 


141 


Lumen 


13 Jan. 1875 


Paul Henry 2 


Paris 


142 


Polana 


28 Jan. 1875 


Palisa 4 


Pola 


*43 


Adria 


23 Feb. 1875 


Palisa 5 


Pola 


144 


Vibilia 


3 June 1875 


Peters 21 


Clinton 


145 


Adeona 


3 June 1875 


Peters 22 


Clinton 


146 


Lucina 


8 June 1875 


Borrelly 6 


Marseilles 


147 


Protogeneia 


10 July 1875 


Schulhof 


Vienna 


148 


Gallia 


7 Aug. 1875 


Pros. Henry 3 


Paris 


149 


Medusa 


21 Sept. 1875 


Perrotin 2 


Toulouse 


150 


Nuwa 


18 Oct. 1875 


Watson 17 


Ann Arbor 


I 5 I 


Abundantia 


1 Nov. 1875 


Palisa 6 


Pola 


152 


Atala 


2 Nov. 1875 


Paul Henry 3 


Paris 


*53 


Hilda 


2 Nov. 1875 


Palisa 7 


Pola 


154 


Bertha 


4 Nov. 1875 


Pros. Henry 4 


Paris 


155 


Scylla 


8 Nov. 1875 


Palisa 8 


Pola 



Small Planets between Mars and Jupiter 401 



NUM- 




DATE OF 


DISCOVERER AND 


PLACE OF 


BER 


NAME 


DISCOVERY 


HIS NUMBER 


DISCOVERY 


I56 


Xantippe 


22 NOV. 1875 


Palisa 9 


Pola 


1 S7 


Dejanira 


i Dec. 1875 


Borrelly 7 


Marseilles 


15S 


Coronis 


4 Jan. 1876 


Knorre 1 


Berlin 


J 59 


^Emilia 


26 Jan. 1876 


Paul Henry 4 


Paris 


160 


Una 


20 Feb. 1876 


Peters 23 


Clinton 


161 


Athor 


19 Apr. 1876 


Watson 18 


Ann Arbor. 


162 


Laurentia 


21 Apr. 1876 


Pros. Henry 5 


Paris 


163 


Erigone 


26 Apr. 1876 


Perrotin 3 


Toulouse 


164 


Eva 


12 July 1876 


Paul Henry 5 


Paris 


165 


Loreley 


9 Aug. 1876 


Peters 2 4 


Clinton 


166 


Rhodope 


15 Aug. 1876 


Peters 25 


Clinton 


167 


Urda 


28 Aug. 1876 


Peters 26 


Clinton 


168 


Sibylla 


27 Sept. 1876 


Watson 19 


Ann Arbor 


169 


Zelia 


28 Sept. 1876 


Pros. Henry 6 


Paris 


170 


Maria 


10 Jan. 1877 


Perrotin 4 


Toulouse 


171 


Ophelia 


13 Jan. 1877 


Borrelly 8 


Marseilles 


172 


Baucis 


5 Feb. 1877 


Borrelly 9 


Marseilles 


l 73 


Ino 


1 Aug. 1877 


Borrelly 10 


Marseilles 


174 


Phaedra 


2 Sept. 1877 


Watson 20 


Ann Arbor 


175 


Andromache 


1 Oct. 1877 


Watson 21 


Ann Arbor 


176 


Idunna 


14 Oct. 1877 


Peters 27 


Clinton 


177 


Irma 


5 Nov. 1877 


Paul Henry 6 


Paris 


178 


Belisana 


6 Nov. 1877 


Palisa 10 


Pola 


179 


Clytemnestra 


11 Nov. 1877 


Watson 22 


Ann Arbor 


180 


Garumna 


29 Jan. 1878 


Perrotin 5 


Toulouse 


181 


Eucharis 


2 Feb. 1878 


Cottenot 


Marseilles 


182 


Elsa 


7 Feb. 1878 


Palisa u 


Pola 


183 


Istria 


8 Feb. 1878 


Palisa 12 


Pola 


184 


Deiopeia 


28 Feb. 1878 


Palisa 13 


Pola 


185 


Eunice 


1 Mar. 1878 


Peters 28 


Clinton 


186 


Celuta 


6 Apr. 1878 


Pros. Henry 7 


Paris 


187 


Lamberta 


11 Apr. 1878 


Coggia 2 


Marseilles 


188 


Menippe 


18 June 1878 


Peters 2 g 


Clinton 


189 


Phthia 


9 Sept. 1878 


Peters ^ 


Clinton 


190 


Ismene 


22 Sept. 1878 


Peters 31 


Clinton 


191 


Kolga 


30 Sept. 1878 


Peters 32 


Clinton 


192 


Nausicaa 


17 Feb. 1879 


Palisa 14 


Pola 


*93 


Ambrosia 


28 Feb. 1879 


Coggia 3 


Marseilles 


194 


Procne 


21 Mar. 1879 


Peters 33 


Clinton 


195 


Eurykleia 


22 Apr. 1879 


Palisa 15 


Pola 



402 



Stars and Telescopes 



NUM- 




DATE OF 


DISCOVERER AND 


PLACE OF 


BER 




DISCOVERY 


HIS NUMBER 


DISCOVERY 


I96 


Philomela 


14 May 1879 


Peters 34 


Clinton 


197 


Arete 


21 May 1879 


Palisa 16 


Pola 


198 


Ampella 


13 June 1879 


Borrelly n 


Marseilles 


199 


Byblis 


9 July 1879 


Peters 35 


Clinton 


200 


Dynamene 


27 July 1879 


Peters 36 


Clinton 


201 


Penelope 


7 Aug. 1879 


Palisa l7 


Pola 


202 


Chryseis 


11 Sept. 1879 


Peters 37 


Clinton 


203 


Pompeia 


25 Sept. 1879 


Peters 38 


Clinton 


204 


Callisto 


8 Oct. 1879 


Palisa 18 


Pola 


205 


Martha 


13 Oct. 1879 


Palisa 19 


Pola 


206 


Hersilia 


13 Oct. 1879 


Peters 39 


Clinton 


207 


Hedda 


17 Oct. 1879 


Palisa 20 


Pola 


208 


Lachrymosa 


21 Oct. 1879 


Palisa 21 


Pola 


209 


Dido 


22 Oct. 1879 


Peters 40 


Clinton 


210 


Isabella 


12 Nov. 1879 


Palisa 22 


Pola 


211 


Isolda 


10 Dec. 1879 


Palisa 23 


Pola 


212 


Medea 


6 Feb. 1880 


Palisa 24 


Pola 


213 


Lilaea 


16 Feb. 1880 


Peters 41 


Clinton 


214 


Aschera 


26 Feb. 1880 


Palisa 25 


Pola 


215 


GEnone 


7 Apr. 1880 


Knorre 2 


Berlin 


2l6 


Cleopatra 


10 Apr. 1880 


Palisa 26 


Pola 


217 


Eudora 


30 Aug. 1880 


Coggia 4 


Marseilles 


2l8 


Bianca 


4 Sept. 1880 


Palisa 27 


Pola 


219 


Thusnelda 


30 Sept. 1880 


Palisa 28 


Pola 


220 


Stephania 


19 May 1881 


Palisa 29 


Vienna 


221 


Eos 


18 Jan. 1882 


Palisa 30 


Vienna 


222 


Lucia 


9 Feb. 1882 


Palisa 31 


Vienna 


223 


Rosa 


9 Mar. 1882 


Palisa 32 


Vienna 


224 


Oceana 


30 Mar. 1882 


Palisa 33 


Vienna 


225 


Henrietta 


19 Apr. 1882 


Palisa 34 


Vienna 


226 


Weringia 


19 July 1882 


Palisa 85 


Vienna 


227 


Philosophia 


12 Aug. 1882 


Paul Henry 7 


Paris 


228 


Agathe 


19 Aug. 1882 


Palisa 36 


Vienna 


229 


Adelinda 


22 Aug. 1882 


Palisa 37 


Vienna 


23O 


Athamantis 


3 Sept. 1882 


De Ball 


Bothkamp 


23I 


Vindobona 


10 Sept. 1882 


Palisa 38 


Vienna 


232 


Russia 


31 Jan. 1883 


Palisa 39 


Vienna 


2 33 


Asterope 


11 May 1883 


Borrelly 12 


Marseilles 


234 


Barbara 


12 Aug. 1883 


Peters 42 


Clinton 


235 


Carolina 


28 Nov. 1883 


Palisa 4 


Vienna 



Small Planets between Mars and Jupiter 403 



WUM- 




DATE OF 


DISCOVERER AND 


PLACE OF 


BEK 




DISCOVERY 


HIS NUMBER 


DISCOVERY 


236 


Honoria 


26 Apr. 1S84 


Palisa 41 


Vienna 


237 


Ccelestina 


27 June T8S4 


Palisa ao 


Vienna 




Hypatia 


1 July 1S84 Knorre 3 


Berlin 




Adrastea 


iS Aug. 18S4 ' Palisa 43 


Vienna 


240 


Vanadis 


27 Aug. 1884 


Borrelly 13 


Marseilles 


241 


Germania 


12 Sept. 1SS4 


Luther 01 


Diisseldorf 


242 


Kriemhild 


22 Sept. 1SS4 Palisa 44 


Vienna 


-43 


Ida 


29 Sept. 1S84 Palisa 45 


Vienna 


244 


Sita 


14 Oct. 1S84 


Palisa 46 


Vienna 


245 


Vera 


6 Feb. 18S5 


Pogson 8 


Madras 


246 


Asporina 


6 Mar. 1885 


Borrelly 14 


Marseilles 


247 


Eukrate 


14 Mar. 18S5 


Luther 22 


Diisseldorf 


24S 


Lameia 


5 June 1S85 


Palisa 47 


Vienna 


249 


Use 


16 Aug. 18S5 


Peters 43 


Clinton 


250 


Bettina 


3 Sept. 1SS5 


Palisa 48 


Vienna 


25 1 


Sophia 


4 Oct. 1S85 


Palisa 49 


Vienna 


252 


Clementina 


11 Oct. 1SS5 


Perrotin 6 


Nice 


2 53 


Matilda 


12 Nov. 18S5 


Palisa 50 


Vienna 


2 54 


Augusta 


31 Mar. 1886 


Palisa 51 


Vienna 


2 55 


Oppavia 


31 Mar. 1 886 


Palisa 62 


Vienna 


256 


Walpurga 


3 Apr. 18S6 


Palisa 53 


Vienna 


257 


Silesia 


5 Apr. 1886 


. Palisa 54 


Vienna 


258 


Tyche 


4 May 1886 


Luther 23 


Diisseldorf 


259 


Altheia 


28 June 1 886 


Peters 44 


Clinton 


260 


Huberta 


3 Oct. 1SS6 


Palisa 55 


Vienna 


261 


Prvmno 


31 Oct. 1SS6 


Peters 45 


Clinton 


262 


Valda 


3 Nov. 1886 


Palisa 56 


Vienna 


263 


Dresda 


3 Nov. 1SS6 


Palisa 57 


Vienna 


264 


Libussa 


17 Dec. 1886 


Peters 46 


Clinton 


265 


Anna 


25 Feb. 1S87 


Palisa 58 


Vienna 


266 


Aline 


17 Mav 1887 


Palisa 59 


Vienna 


267 


Tirza 


27 May 1887 


Charlois x 


Nice 


268 


Adorea 


9 June 1S87 


Borrelly 15 


Marseilles 


269 


Justitia 


21 Sept. 1887 


Palisa 60 


Vienna 


270 


Anahita 


8 Oct. 1887 


Peters 47 


Clinton 


271 


Penthesilea 


13 Oct. 1887 


Knorre 4 


Berlin 


272 


Antonia 


4 Feb. 188S 


Charlois a 


Nice 


273 


Atropos 


8 Mar. 1888 


Palisa 61 


Vienna 


274 


Philagoria 


3 Apr. 1888 


Palisa 62 


Vienna 


275 


Sapientia 


15 Apr. 1888 


Palisa C3 


Vienna 



404 



Stars and Telescopes 



NUM- 


NAME 


DATE OF 


DISCOVERER AND 


PLACE OF 


BER 


DISCOVERY 


HIS NUMBER 


DISCOVERY 


276 


Adelheid 


17 Apr. 1888 


Palisa 64 


Vienna 


277 


Elvira 


3 May 1888 


Charlois 3 


Nice 


278 


Paulina 


16 May 1888 


Palisa 65 


Vienna 


279 


Thule 


25 Oct. 1888 


Palisa 66 


Vienna 


280 


Philia 


29 Oct. 1888 


Palisa 67 


Vienna 


28l 


Lucretia 


31 Oct 1888 


Palisa 68 


Vienna 


282 


Clorinda 


28 Jan. 1889 


Charlois 4 


Nice 


283 


Emma 


8 Feb. 1889 


Charlois 5 


Nice 


284 


Amelia 


29 May 1889 


Charlois 6 


Nice 


285 


Regina 


3 Aug. 1889 


Charlois 7 


Nice 


286 


Idea 


3 Aug. 1889 


Palisa 69 


Vienna 


287 


Nephthys 


25 Aug. 1889 


Peters 48 


Clinton 


288 


Glauca 


20 Feb. 1890 


Luther 24 


Diisseldorf 


289 


Nenetta 


10 Mar. 1890 


Charlois 8 


Nice 


290 


Bruna 


20 Mar. 1890 


Palisa 70 


Vienna 


291 


Alice 


25 Apr. 1890 


Palisa 71 


Vienna 


292 


Ludovica 


25 Apr. 1890 


Palisa 72 


Vienna 


293 


Brasilia 


20 May 1890 


Charlois 9 


Nice 


294 


Felicia 


15 July 1890 


Charlois 10 


Nice 


295 


Theresia 


17 Aug. 1890 


Palisa 73 


Vienna 


296 


Phaethusa 


19 Aug. 1890 


Charlois n 


Nice 


297 


Cecilia 


9 Sept. 1890 


Charlois 12 


Nice 


298 


Baptistina 


9 Sept. 1890 


Charlois 13 


Nice 


299 


Thora 


6 Oct. 1890 


Palisa 74 


Vienna 


300 


Geraldina 


3 Oct. 1890 


Charlois 14 


Nice 


301 


Bavaria 


16 Nov. 1890 


Palisa 75 


Vienna 


302 


Clarissa 


14 Nov. 1890 


Charlois 15 


Nice 


303 


Josephina 


12 Feb. 1891 


Millosevich 1 


Rome 


304 


Olga 


14 Feb. 1891 


Palisa 76 


Vienna 


305 


Gordonia 


16 Feb. 1891 


Charlois 16 


Nice 


306 


Unitas 


1 Mar. 1891 


Millosevich 2 


Rome 


3°7 


Nike 


5 Mar. 1891 


Charlois l7 


Nice 


308 


Polyxo 


31 Mar. 189 1 


Borrelly 16 


Marseilles 


309 


Fraternitas 


6 Apr. 1891 


Palisa 77 


Vienna 


310 


Margarita 


16 May 1891 


Charlois 18 


Nice 


3" 


Claudia 


11 June 1891 


Charlois 19 


Nice 


312 


Pierretta 


28 Aug. 1891 


Charlois 2 o 


Nice 


313 


Chaldaea 


30 Aug. 1891 


Palisa 78 


Vienna 


3i4 


Rosalia 


1 Sept. 1891 


Charlois 21 


Nice 


3i5 


Constantia 


4 Sept. 1891 


Palisa 79 


Vienna 



Small Planets between Mars and Jupiter 405 







DATE OF 


DISCOVERER AND 


PLACE OF 


BER 


NAME 


DISCOVERY 


HIS NUMBER 


DISCOVERY 


3l6 


Goberta 


S Sept. 1 891 


i 

Charlois 22 


Xice 


3 l 7 


Roxana 


11 Sept. 1891 


Charlois 23 


Xice 


318 


Magdalena 


24 Sept. 1891 


' Charlois 24 


Xice 


3*9 


Leona 


8 Oct. 1891 


Charlois 05 


X'ice 


320 


Katharina 


11 Oct. 1S91 


Palisa 80 


Vienna 


321 


Florentina 


15 Oct. 1891 


Palisa 81 


Vienna 


322 


Phaeo 


27 Nov. 1S91 


Borrellv l7 


Marseilles 


3 2 3 


Brucia 


20 Dec. 1S91 


WO^ 


Heidelberg 


3 2 4* 


Bamberga 


25 Feb. 1892 


Palisa 39 


Vienna 


325 


Heidelberga 


4 Mar. 1892 


Wolf a " 


Heidelberg 


326 


Tamara 


19 Mar. 1892 


Palisa 8 3 


Vienna 


3 2 7 


Columbia 


22 Mar. 1892 


Charlois 05 


X'ice 


328 


Gudrun 


iS Mar. 1S92 


Wolf 3 


Heidelberg 


3 2 9 


Svea 


21 Mar. 1S92 


Wolf 4 


Heidelberg 


330 


Adalberta 


iS Mar. 1S92 


Wolf 5 


Heidelberg 


33i 


Etheridgea 


1 Apr. 1892 


Charlois 27 


X'ice 


332 Siri 


19 Mar. 1892 


Wolf 6 


Heidelberg 


333 Badenia 


22 Aug. 1S92 


Wolf - 


Heidelberg 


334 Chicago 


23 Aug. 1892 


Wolf 8 


Heidelberg 


335 


Roberta 


1 Sept. 1S92 


Staus 1 


Heidelberg 


33^ 


Lacadiera 


19 Sept. 1S92 


Charlois 23 


X T ice 


Devosa 


22 Sept. 1892 


Charlois 29 


X'ice 


53$ 


Boudrosa 


25 Sept. 1892 


Charlois 3) 


X'ice 


339 


Dorothea 


25 Sept. 1S92 


Wolf 9 


Heidelberg 


340 


Eduarda 


25 Sept. 1892 


Wolf 10 


Heidelberg 


34i 


California 


25 Sept. 1S92 


Wolf n 


Heidelberg 


342 


Endymion 


17 Oct. 1S92 


Wolf 12 


Heidelberg 


343 


Ostara 


15 Nov. 1892 


Wolf lf 


Heidelberg 


344 


Desiderata 


15 Nov. 1892 


Charlois 31 


X'ice 


345 


Tercidina 


23 Nov. 1892 


Charlois 32 


Xice 


346 


Hermentaria 


25 Nov. 1892 


Charlois 33 


X'ice 


347 


Pariana 


28 Nov. 1S92 


Charlois 34 


X'ice 


348 


May 


2S Nov. 1S92 


Charlois 35 


X'ice 


349 


Dembowska 


9 Dec. 1S92 


Charlois 36 


Xice 


35° 


Ornamenta 


14 Dec. 1S92 


Charlois 3 - 


Xice 


35i 


Vrsa 


16 Dec. 1S92 


Wolf y 


Heidelberg 


352 


Gisela 


12 Jan. 1893 


Wolf 15 


Heidelberg 


353 


1893 F 


16 Jan. 1893 


Wolf 16 


Heidelberg 


354 


Eleonora 


1- Jan. 1S93 


Charlois 33 


X'ice 


355 


1893^ 


20 Jan. 1893 


Charlois 39 


X'ice 



1 Nearly all the discoveries following 324 have been made photographically. 



406 



Stars and Telescopes 



NUM- 
BER 



356 

357 
358 
359 
360 

361 
362 
3 6 3 
364 
365 

366 

367 
368 

3 6 9 
370 

37i 
372 
373 
374 
375 

376 

377 
378 
379 
380 

38i 

382 

383 
384 
385 

386 

387 
388 

389 
39o 

39i 
392 
393 
394 
395 



893S 
893/ 
893^ 

803 M 

893^ 

893 P 

893^ 
893^ 

893^ 

893 V 

893 w 

893 A A 
893 \AB 
Aeria 
893 AC 

893 AD 
893 AH 
%93AJ 
^3AK 
893 AL 

893 AM 
893 AN 

893 AP 
S94AQ 
S94AP 

894 AS 
894 AT 
S94AU 

Burdigala 
Ilmatar 

1894 A Y 
1894 AZ 
1894 BA 
1894 BB 
1894 BC 

Ingeborg 
Wilhelmina 
1894 BG 
1894 BH 
1894 BK 



DATE OF 
DISCOVERY 



21 Jan. 1893 

11 Feb. 1893 

8 Mar. 1893 

10 Mar. 1893 

11 Mar. 1893 

11 Mar. 1893 

12 Mar. 1893 

17 Mar. 1893 
19 Mar. 1893 
21 Mar. 1893 

21 Mar. 1893 
19 May 1893 
19 May 1893 

4 July 1893 
14 July 1893 

16 July 1893 

19 Aug. 1893 
14 Sept. 1893 

18 Sept. 1893 
18 Sept. 1893 

18 Sept. 1893 

20 Sept. 1893 

6 Dec. 1893 
8 Jan. 1894 
8 Jan. 1894 

10 Jan. 1894 
29 Jan. 1894 

29 Jan. 1894 

11 Feb. 1894 
I Mar. 1894 

1 Mar. 1894 

5 Mar. 1894 

7 Mar. 1894 

8 Mar. 1894 
24 Mar. 1894 

1 Nov. 1894 
4 Nov. 1894 
4 Nov. 1894 

19 Nov. 1894 

30 Nov. 1894 



DISCOVERER AND 
HIS NUMBER 



Charlois 40 
Charlois 4l 
Charlois 42 
Chark)is 43 
Charlois 44 

Charlois 45 
Charlois 46 
Charlois 47 
Charlois 48 
Charlois 49 

Charlois 50 
Charlois 51 
Charlois 52 
Borrelly 18 
Charlois 53 

Charlois 54 
Charlois 55 
Charlois 56 
Charlois 57 
Charlois 58 

Charlois 59 
Charlois 60 
Charlois 61 
Charlois 62 
Charlois 63 

Charlois 64 
Charlois 65 
Charlois 66 
Courty x 
Wolf 17 

Wolf 18 
Courty 2 
Charlois 67 
Charlois 68 
Bigourdan x 

Wolf 19 
Wolf 20 
Wolf 21 
Borrelly 19 
Charlois e9 



PLACE OF 
DISCOVERY 



Nice 
Nice 
Nice 
Nice 
Nice 

Nice 
Nice 
Nice 
Nice 
Nice 

Nice 
Nice 
Nice 
Marseilles 

Nice 

Nice 
Nice 
Nice 
Nice 
Nice 

Nice 
Nice 

Nice 
Nice 
Nice 

Nice 
Nice 
Nice 

Bordeaux 
Heidelberg- 
Heidelberg 
Bordeaux 
Nice 
Nice 
Paris 

Heidelberg 

Heidelberg 

Heidelberg 

Marseilles 

Nice 



Small Planets betiveen Mars and ynpitcr 407 



NUM- 




DATE OF 


DISCOVERER AND 


PLACE OF 


BER 




DISCOVERY 


HIS NUMBER 


DISCOVERY 


396 


iS94^Z 


i Dec. 1894 


Charlois 70 


Nice 


397 


1S94 BJf 


19 Dec. 1894 


Charlois 71 


Nice 


39^ 


1S94 BN 


28 Dec. 1894 


Charlois * 2 


Nice 


399 


1895 BP 


23 Feb. 1895 


Wolf 22 ' 


Heidelberg 


400 


iSg$BC/ 


15 Mar. 1895 


Charlois 73 


Nice 


401 


Ottilia 


16 Mar. 1895 


Wolf 23 


Heidelberg 


402 


iSgsBW 


21 Mar. 1895 


Charlois 74 


Nice 


403 


1895 BX 


18 May 1895 


Charlois 75 


Nice 


404 


i*9SBY 


20 June 1895 


Charlois 76 


Nice 


.405 


1895 BZ 


23 July 1895 


Charlois 77 


Nice 


406 


1895 CB 


23 Aug. 1895 


Charlois 78 


Nice 


407 


1895 CC 


13 Oct. 1895 


Wolf 24 


Heidelberg 


40S 


1895 CD 


13 Oct. 1895 


Wolf 25 


Heidelberg 


409 


1895 CE 


9 Dec. 1895 


Charlois 79 


Nice 


410 


1896 CH 


7 Jan. 1896 


Charlois 80 


Nice 


411 


1896 CJ 


7 Jan. 1896 


Charlois 81 


Nice 


412 


Elisabetha 


7 Jan. 1896 


Wolf 26 


Heidelberg 


4i3 


Edburga 


7 Jan. 1896 


Wolf 2 7 


Heidelberg 


414 


1896 CAT 


16 Jan. 1896 


Charlois 82 


Nice 


4i5 


1896 CO 


7 Feb. 1896 


Wolf 28 


Heidelberg 


416 


Vaticana 


4 May 1896 


Charlois 83 


Nice 


4i7 


1896 CT 


6 May 1896 


Wolf 09 


Heidelberg 


418 


1896 CV 


3 Sept. 1896 


Wolf 30 


Heidelberg 


419 


1896 CW 


3 Sept. 1896 


Wolf 31 


Heidelberg 


420 


Bertholda 


3 Sept. 1896 


Wolf 32 


Heidelberg 


421 


Zahringia 


3 Sept. 1896 


Wolf 33 


Heidelberg 


422 


Berolina 


8 Oct. 1896 


Witt ! _ 


Berlin 


423 


1896 DB 


7 Dec. 1896 


Charlois 84 


Nice 


424 


1896 DF 


31 Dec. 1896 


Charlois 85 


Nice 


425 


1896 DC 


28 Dec. 1896 


Charlois 83 


Nice 


426 


1897 DH 


25 Aug. 1897 


Charlois 87 


Nice 


427 


1897 DJ 


27 Aug. 1897 


Charlois 88 


Nice 


428 


Monachia 


18 Nov. 1897 


Villiger a 


Munich 


429 


1897 DL 


23 Nov. 1897 


Charlois 89 


Nice 


43° 


1897 DM 


18 Dec. 1897 


Charlois 90 


Nice 


43 1 


1897 DAT 


18 Dec. 1897 


Charlois 91 


Nice 


43 2 


1897 DO 


18 Dec. 1897 


Charlois 92 


Nice 


433 


Eros 


13 Aug. 1898 


Witt 


Berlin 


434 


Hungaria 


11 Sept. 1898 


Wolf M 


Heidelberg 


435 


1898 DS 


11 Sept. 1898 


*Wolf&S 35 


1 Heidelberg 



408 



Stars and Telescopes 



NUM- 




DATE OF 


DISCOVERER AND 


PLACE OF 


BER 




DISCOVERY 


HIS NUMBER 


DISCOVERY 


436 

433 
439 

440 


1898 DT 
1898 DU 
1898 DV 
1898 DW 
1898 DX 


13 Sept. 1898 
8 Nov. 1898 
6 Nov. 1898 
6 Nov. 1898 
6 Nov. 1898 


* Wolf & S 36 
Charlois 93 
Wolf & S 37 

* Wolf & V 38 

Wolf & V 39 


Heidelberg 

Nice 

Konigstuhl 

Konigstuhl 

Konigstuhl 


441 
442 

443 
444 
445 


iSgS DY 
1898 DZ 
1898 EA 
1898 EB 
1898 EC 


13 Nov. 1898 
19 Nov. 1898 
19 Nov. 1898 

13 Oct. 1898 

14 Oct. 1898 


Wolf & V 4 
Wolf & V 41 

Wolf & S 42 

Coddington 1 
Coddington 2 


Konigstuhl 
Konigstuhl 
Konigstuhl 
Mt Hamilton 
Mt Hamilton 


446 

447 
448 


1898 ED 

1899 EE 
1899 EF 


8 Dec. 1898 
15 Feb. 1899 
17 Feb. 1899 


Charlois 94 
Wolf & S 43 
Wolf&S 44 


Nice 

Konigstuhl 

Konigstuhl. 


449 

450 J 











Planet (433) Eros possesses exceptional interest because of the large eccen- 
tricity of its orbit, and its mean distance of only 1.46, that of Mars being 1.52. 
But it is not proper to describe the path of Eros as lying within that of Mars, 
because the perihelion points of the two orbits lie on opposite sides of the 
Sun. Only about half of Eros's path, therefore, is within that of Mars : but 
so eccentric is the orbit that it approaches within 14 million miles of our own 
path round the Sun. When Eros comes to opposition near the time of 
perihelion, as must have been the case in 1894, its stellar magnitude is about 
the 7th, or almost within naked-eye visibility. Professor Pickering and 
Mrs Fleming have re-discovered the planet on about 20 Harvard plates 
exposed near this time, greatly enhancing the accuracy of the orbit calculated 
by D* Chandler. Not until 1924 does so favorable an opposition again 
occur; but in December 1900 it will approach us within 31 million miles, or 
about four million miles nearer than Mars ever does. This opposition will 
give a new and very accurate value of the solar parallax, because of the 
precision with which a diskless object of this sort can be measured. The 
opposition of 1924 will provide a value of the Sun's distance far exceeding 
in accuracy that from all other methods now available. Probably Eros is 
less than 20 miles in diameter, and its close approach to the Earth every 30 
years will introduce perturbations of its motion of great interest to gravi- 
tational astronomers. It consumes if years in journeying once completely 
round the Sun; and its variation between such wide extremes of distance 
suggests many important problems to the astrophysicist. 



* S. or V. signifies that Dr Wolf was assisted by Sc:.wassmann or 
Villiger in making the discovery. 



INDEX 



Note. — The figures in parentheses are numbers of small planets 



Abbe 332 

Aberration 43, 45, 47 
Abetti 179 
Abney 74 

Abundantia (151) 400 
Adalberta (330) 405 
Adams viii, 27 ,(p ortraits) 

143, 385 ; 144, i54> 229 
Adams, M r s viii 
Adelheid (276) 404 
Adelinda (229) 402 
Adeona (145) 400 
Adorea (268) 403 
Adrastea (239) 403 
Adria (143) 400 
iEgina(gi) 399 
-dEgle (96) 399 
./Emilia (159) 401 
Aeria (369) 406 
Aerolites 214 
jEthra (132) 113, 400 
iEtius 186 
Agathe (228) 402 
Aglaia (47) 398 
Airy 27, 65, 100, (portr.) 

102, 103, 356 
Albatenius 10 
Albrecht 25 
Alceste (124) 400 
Alcmene (82) 399 
Aletheia (259) 403 
Alexander, S. 103 
Alexander in. 337 
Alexandra (54) 398 
Algue" 392 
Alice (291) 404 
Aline (266) 403 
Allegheny Obs. vi 
Allis 347 
Almagest 10 
Almucantar 371 
Al-Sfifi 10, 308 
Althaea (119) 400 



Amalthea (113) 399 
Ambronn 148 
Ambrosia (193) 401 
Amelia (284) 404 
Am. Book Co. vii, 265, 

280 
Amherst College 223 
Amherst Eel. Exp. 363 
Ampella (198) 402 
Amphitrite (29) 397 
Anahita (270) 403 
Anaxagoras 244 
Anaximander 244 
Anaximenes 244 
Anderson 267 
Andes 395 
Anding 152 
Andre 391 
Andromache (175) 115, 

401 
Andromeda nebula 243 
Andromedes 219 
Angelina (64) 398 
Angot 25, 391 
Angstrom 72, 73, 80 
Anna (265) 403 
Anthelme 266 
Antigone ( 129) 400 
Antiope (90), 399 
Antonia (272) 403 
Antoniadi 149, 168, 171, 

I 79 
Aphelion 54 
Apian 187, 188 
Appleton vii, 386, 391 
Arabians, astron. of 10 
Arago opp. 26, {portr.) 

a 155 
Aratus 9 

Arcturus 203 

Arequipa, Peru 264, 299 

Arete (197) 402 

Arethusa (95) 399 



Argelander {portr.) 261,, 

262, 272, 305 
Argus, 7] 265, 269, 350 
Ariadne (43) 398 
Ariel 138 
Aristotle 155, 244 
Arnold 373 
d' Arrest 149, 193, 197; 

308, 311, 399 
Artemis (105) 399 
Aschera (214) 402 
Asia (67) 398 
Asporina (246) 403 
v. Asten 191, 206 
Asteroids (see planets) 
Asterope (233) 402 
Astrasa (5) 114, 397 
Astrographic Survey 260 
Astrolabe 390 
Astrology 1 

Astronomer Royal vi, 39 
A stronomical Journal vi 
Astronomy, practical 396 
Astrophysical Jour, vi, 

33, 81, 147,179,315,394 
Atala (152) 400 
Atalanta (36) 398 
Ate (111) 399 
Athamantis (230) 402 
Athor (161) 401 
Atropos(273) 403 
Attila 186 
Augusta (254) 403 
Aurelius 10 

Aurora 25, 67 ; (94) 399 
Ausonia (63) 398 
Austria (136) 400 
Auwers 53, 55, 149, 276,. 

283 

Bache telescope 299, 349^ 

35i 
Backhouse 230 



4io 



Index 



Backlund 130, 149, 151, 

iqi, 192, 206 
Badenia (333) 405 
Bailey, F. H. 241 ; S. I. 

265, 271, 309, 312 
Baillaud 152 

Bailly 18, {portr.) opp. 18 
Bakhuyzen 178 
Baldwin 391 
Ball, Sir R. S. 25, 68, 82, 

179-80,229-30. 241,254, 

276, 312-13,315; W. 132 
Bamberg 339 
Bamberga (324) 405 
Baptistina (298J 404 
Barbara (234) 402 
Barnard vii, viii, 86, 108, 

in, 114, 117, 120, 121, 

124-5,128, 134, 151,153? 

179, 194, 196-7, opp. 200, 

201, 207, 218, 228, 230, 

256, 268, 309, 354, 358 

-9, 387, 394 
Bartlett 343 
Battermann 53 
Baucis (172) 401 
Bausch and Lomb 319 
Bauschinger 147 
Bavaria (301) 404 
Bayer 232, 233, 240,269 
Beatrix (83) 399 
Becker,E. 390 ; G. F. 25 ; 

L. 73, 80 
Becquerel 74 
Beer 26, 155, 165 
Belisana (178) 401 
Bellona (28) 397 
Belopolsky 151, 313 
Bentley 18 
Benzenberg 228 
Berberich 207 
Berolina (422) 407 
Bertha (154) 400 
.Bertholda (420) 407 
Bertin 18 
Bessel 88, 136, 152, 185, 

206, 261, {portr.) 273, 

2 74-5, 278, 287 
Bettina (250) 403 
Bianca (218) 402 
Bianchini no, 155 
Biela 191, 192, 219 
Bienewitz 187 
Bigourdan 162, 406 
Biot 18, 222, 228 
Birmingham 266 
Bischoffsheim 169, 331 
Bishop 25 
Black, A. & C. vii 
Boeddicker 33, 304, 312 
Bolometer 74 
Bond, G. P. 128, 132, 151, 

203,206,238,343-4,393; 



J. J. 40; W. C. 128. 

129, 132, 238, {portr.) 

240, 329 
Bonney 25 
Bonpland 209 
Borrelly 399-406 
Boss 206, 312 
Bossert 289 
Boudrosa (338) 405 
Bouvard 140 
Bowditch ( portr.) 374 
Boy den {portr.) 381 
Boyden Obs. 379, 382 
Boys 103 
Bradley 45, {portr.) 46, 

100, 283 
Brashear vi, 321-2, 324, 

342,346,352 4, 388, 390 
Brasilia (293) 404 
Braun 254 
Bredichin 150, 185, 205, 

206, 230 
Breen 103 
Bremiker 144 
Brenner 149, 151, 167-8, 

*79, 37 6 "7> 39 6 ' 
Brester 79, 81 
Brewster 80, 180 
Brezina 229 
Brinkley 272 
British Museum 221, 225 
Brodie 205 
Brooks 184, 188-9, I 9 6_ 7> 

201, 214, 218, 325 
Brorsen 193, 197, 228 
Brothers 394 
Bruce, Miss 263 
Bruce telescope 264, 351 
Brucia (323) 405 
Briinnow (portr.) 275, 2 76 
Bruna (290) 404 
Brunhilda (123) 400 
Buchholtz 153 
Buchner 229 
Buff and Berger 369 
Bulletin Astron. vi, 207 
Bunsen 16 
Burckh alter 364 
Burdigala (384) 406 
Burnham 283-4, 3 I 3, 343* 

386 
Burr 180 
Burrard 89 
Burritt 241 
Byblis (199) 402 
Byrd 375 
Byrne 331 

Calcium, opp. 64, 78 
Calendar 34 
California (341) 405 
Callandreau 149, 207 
Calliope (22) 397 



Callisto 121 ; (204) 402 
Calver 388 
Calypso (53) 398 
Camilla (107) 399 
Campani 132 
Campbell, J. 343; W. W. 

124, 151, 174, 175, i 79 , 

268, 289, 313, 346, 389, 

396 
Canon der Finsternisse 

opp. 86, 89 
Capella, spectrum 301 
Cape Town, Royal Obs. 

259 
Carinae, Eta 265, 269, 
^350 
Carl 206 

Carolina (235) 402 
Carpenter 33 
Carrington 56, 67 
Cassandra (114) 399 
Cassini 12, 43, 117, 120, 

129, 132, {portr.) opp, 

132, 155, 227, 266 
Cauchoix 331 
Cecilia (297) 404 
Celuta(i86) 4 oi 
Ceraski 313 
Ceres (1) 114, 397 
Cerulli 171, 179 
Chacornac 241, 397-8 
Chaldasa (313) 404 
Challis 144 
Chamberlin 254 
Chambers 18, 40, 89, 147, 

207,312, 313, 386, 391, 

393, 396 
Chance Bros. 328 
Chandler vi, 24, opp. 24, 

25, 149, 196, 262, 271, 

312, 313, 37 I_ 2, 390 
Chapman 71 
Charles 11. 39 ; v. 198 
Charlois viii, 15, 115, 149, 

403-8 
Chase, F. L. 313 ; P. E. 

103 
Chauvenet 396 
Chicago (334) 405 
Childrey 227 
Chladni {portr.) 208, 

228 
Christian viii. 203 
Christie vi, 39 
Chromosphere opp. 64, 65 
Chronograph 390 
Chronometer 372, 389, 390 
Chryseis (202) 402 
Circe (34) 397 
Clacey 331 
Clarissa (302) 404 
Clark, A. 8, 133, 33<>, 332, 

334, {portr.) 335, 346; 



Index 



411 



A. G. 133,283, (/Wr.) 
285, 334, 336, 349, 353, 
356, 3S4-0; G. B. 8, 
133, 263, 334, (portr.) 
336; L. 241, 390 
•Clarke, A. R. 25; H. L. 

313 ; J. F. 241 
Claudia (311) 404 
Clementina (252) 403 
Cleopatra (216) 402 
Gierke, A. M. iS, 81, 89, 

148, 207, 254, 295, 312- 
M, 3S8, 390,39!; E - M - 

149, 151 
Clifford 253 
Clio (S4) 399 
Clorinda (282) 404 
Clotho (97) 399 
Clusters (see Stars) 
Clymene (104) 399 . 
Clytemnestra (179) 401 
Clytia (73) 398 
Coakley 254 
Coelestina (237) 403 
Ccelostat 390-1 

Coggia 183-4, 201, 203-4, 
399, 401-2 

Colas 240, 396 

Colbert 241 

Colin 392 

Columbia (327) 405 

Comets, 98, 181 ; bibliog- 
raphy 206-7 I Biela's 
191, 219 ; Brooks's 184, 
218 ; Brorsen's 193 ; 
Coggia's2oi, 203 ; com- 
position 185, 204; d'Ar- 
rest's 193 ; De Vico's 
195 ; disintegration 217; 
doctrine of 186 ; Do- 
nates 184, 203 ; eclipse 
202 ; Encke's 188-92 ; 
Faye's 193 ; Finlay's 
195 ; Gale's opp. 200 ; 
Halley's 181, 199 ; head 
183 ; Holmes's 196 ; 
Lexell's 196 ; literature 
187 ; number 183, 198 ; 
of 1680 181 ; of 1843 
199; of 1882 200; or- 
bits 181-3 ; periodic 
184-97; photographs 86, 
194, opp. 200, 202, 358 
-9 ; Pons's 188 ; returns 
of 197 ; spectra 204 ; 
Swift's 194 ; tails 185, 
205 ; Tempel's 194, 205 ; 
Tewfik 202 ; Tuttle's 
193 ; visibility 185 ; 
Wolfs 195 

Common 200, 323, 326, 
386, 388, 393 

Commutators 361, 363 



Com stock 160, 161, 179, 

396 
Comte 253 
Concordia (58) 398 
Conroy 387 
Constantia (315) 404 
Constantine v. 187 
Constellations 231 
Cooke 33 r, 387 
Copeland 32, 205-6, 227, 

392, 395 
Copernican system 10 
Copernicus 10, (portr.) 11 
Cordier 221 
Cornu 44, 73, 76, 80 
Corona 79, 86, 87, 89 

photography of 360-3 
Coronis (158) 401 
Coronium 79 
Corrigan 147 
Cosmogony 242 
Cottam 241 
Cottenot 401 
Coude opp. 30, 340 
Coulvier-Gravier 228 
Courty 406 
Crabtree 108 
Crew 56 
Croll 254 
Crommelin 149 
Crossley 311, 323 
Cruls 53, 149 
Cycle, Celestial 396 
Cyrene (133) 400 
Cysat 307 

Dan^e (61) 398 
Daphne (41) 398 
Darwin 106, 136, 152, 248, 

249, 250, 251, 253-4 
Daubree 221, 229, 230 
Davis, C. H. 99; C. H. 

jr- 390 
Dawes 123, 128, 151, 156 

-7, 165, (portr.) 283, 

334-5 
Dawson 25 

Day, sid. and solar 21 
De Ball 402 
De Damoiseau 150 
De Gasparis 397-9 
Deichmuller 207 
Deimos 112 
Dejanira (157) 401 
Dejopeja (184) 401 
Delambre 18, (portr.) 

opp. 18 
De la Rue 393 
Delaunay (portr.) opp. 26, 

27 
Dembowska (349) 405 
Dembowski 283 
Democritus 244 



Denning vii, 30, 107, no, 

118, 151, 193, 197, 198, 

207, 211, 214-16, 230, 

386-7, 396 
Desiderata (344) 405 
Deslandres vi, 63, opp. 64, 

86, 297, 301, 314, 315, 

339, 394 
De Vico 1 10, 195, 197 
Devosa (337) 405 
Dewar 68, 74 
Diana (78) 399 
Dido (209) 402 
Dike (99) 399 
DionCassius 185-6 
Dione 129 ; (106) 399 
Dividing engine 369 
Dollond (portr.) 328 
Dominical Letter 38 
Donati 184, 203, 204 
Doolittle 25, 396 
Doppler 56, 285, (portr.) 

286, 289 
Doris (48) 398 
Dorothea (339) 405 
Douglass opp. 108, 123, 

149, 151, 157, 162-3, 165 

-7, 173, i75,i79,3i4,395 

Downing 25, 150 

DQ (see Eros) 

Draper, H. 16, 30, 76, 
201, 204, 297, (portr.) 
298, 309, 312, 322, 325- 
6 , 388, 393 ; Mrs H. vi, 
298 ; J. W. 30, 74, 80 

Dresda (263) 403 

Drew opp. 108 

Dreyer vii, 156, 308, 312, 
39i 

DuneV 56-7, 68, 314 

Dunthorne 198 

Dynamene (200) 402 

Earnshaw 373 
Earth, density 24 

form 19 

motions 23 

size 20 
Easter Day 40 
Eastman 315 
Easton 312, 314 
Echo (60) 398 
Eclipses, solar 4, 82 

bibliography 88-9 

duration 84 

future 88 

photographs 86-7, 89 

photography (auto- 
matic) 360-3 

prediction 84, opp. 86, 
88, opp. 88 

recent 85 
Edburga (413) 407 



412 



Index 



Edgecomb 325 
Eduarda (340) 405 
Egeria (13) 397 
Eichelberger 152 
Elagabalus 186 
Electra (130) 400 
Elements in Sun 72 ; of 

orbit 96, 102 
Eleonora (354) 4°5 
Elger 33 

Elisabetha (412) 407 
Elkin 53, 200, 212, 274, 

278, 279, 311, 360 
Ellery 179 
Elsa (182) 401 
Elvira (277) 404 
Emma (283) 404 
Enceladus 129 
Encke 50, 51, 132, 188, 

189, {portr.) 190, 191, 

192, 197 
Endymion (342) 4°5 
d'Engelhardt 313 
Engelmann, R. 150, 312, 

386 ; W. vii 
Eos (221) 402 
Ephemeris 22, 84, 100, 

115, 122 
Epping 18 

Equatorial {see Telescope) 
Erato (62) 398 
Ericsson 76, 77 
Erigone (163) 401 
Eros (433) s, 53, 113,407-8 
Espm 33,241, 378,396 
Etheridgea (331) 405 
Eucharis (181) 401 
Eukrate (247) 403 
Eudora (217) 402 
Eudoxus 9 
Eugenia (45) 398 
Euler 95, {portr.) 96, 327 
Eunike (185) 401 
Eunomia (15) 397 
Euphrosyne (31) 397 
Europa 121 ; (52) 398 
Euryclea (195) 401 
Eurydice (75) 398 
Eurynome (79) 399 
Euterpe (27) 397 
Eva (164) 401 
Everett 313 
Eyepieces 341 

Fabricius 56, 269 
Fargis37i 
Farrington 230 
Faye 193, 197, 253 
Feil 328 

Felicia (294) 404 
Felicitas (109) 399 
Fenyi6 3 , 68 
Ferguson 397-8 



Feronia (72) 398 
Fides (37) 398 
Field-glass 3 19 
Fievez 68, 72, 80 
Finlay 195, 197, 200, 347 
Fitz 330 
Fizeau 178 

Flagstaff Obs. opp. 108 
Flammarion vii, in, 112, 

149, 151, 158, 161, 168, 

178-80, 313 
Flamsteed 12, 50, 137, 232 
Flaugergues 155 
Fleming, Mrs 268 
Fletcher, L. 229 ; W. I. 

88, 180, 207 
Flight 230 . 
Flora (8) 3 97 
Florentina (321) 405 
Foerster 398 
Fontana 155 
Fontenelle 180 
Fontsere y Riba 68 
Forbes 44, 103, 148 
Fortuna ( 19) 397 
Foucault 44, {portr.) 47, 

324 

Fowler 25, 314, 387, 396 
Fraissinet 394 
Fraternitas (309) 404 
Fraunhofer 16, {portr.) 

17, 80, 32879, 350 
Fraunhofer lines 16, 70 
Freeman 151, 152 
Freia (76) 399 
Frigga {77) 399 
Frisby 312 
Frost 76, 81, 103, 207, 291, 

3i3, 389 

Galatea (74) 398 

Gale 201 

Galileo n, {portr.) 12, 

104, 119, 121, 131, 155, 

297, 316-9 
Galle 132, 144, 207 
Gallia (148) 400 
Ganymede 121 
Garumna (180) 401 
Gassendi {portr.) 104 
Gauss {portr.) 99, 332 
Gautier, M. P. 331, 388; 

R. 194 
Gegenschein 228 
George in. 13, 137 
Georgium Sidus 137 
Geraldina (300) 404 
Gerda (122) 400 
Gerigny 178 
Gerland 254, 387 
Germania (241) 403 
Giberne 313 
Gibson 396 



Gilbert 32 

Gill vi, 53, 206, 260, 274,. 

309,311-3,347.349,376, 

386, 390, 391, 393, 394 ;. 

Mrs 53 
Ginzel 89 
Gisela(3S2)4o5 
Gladstone 103 
Glaisher 229 
Glasenapp 25, 150 
Glass, new Jena 332 
optical 328, 387 
Glauca (288) 404 
Gledhill 120, 311 
Goberta (316) 405 
Godfray 390 
Golden Number 37 
Goldschmidt 195, 397-8 
Goldthwaite 240 
Gordonia ( 305 ) 404 
Gore, J. E. 81, 152, 240, 

254, 312-14; J. H. 25 
v. Gothard 268, 309 
Gould 145, 149, 154, 241^ 

{portr.) 262, 263, 306, 

3M,393 
Graham, A. 397 ; T. 229 
Grant 18, 241, 311, 386 
Gratings 71, 389 
Gravitation 90, 94 
Gravity 94 
Gray 77, 81 
Green, A. H. 254 ; N. E. 

151, 152, 156, 178 
Greene 396 

Greeks, astronomy of 9 
Greenwich Observatory 

39, opp. 64, 100, 333 
Greg 229 
Gregory, J. 320; R. A. 

154* 279 
Groombridge 287 
Grubb, H. vi, 259, 323,. 

333, 354, 387, 39o; T. 

322, {portr.) 323, 386,. 

388 
Grunow 75 
Gudrun (328) 405 
Guillaume 66 
Guillemin 33, 180, 206 
Guinand 328 
Gundlach 387 
Gylden 20S, {portr.) 276,. 

279 

Hagen 271, 315, 390 
Hale vi, 63-5, 80-1, 352,. 

354, 387-9. 392 
Hall, A. 112, 178, 311; 

A. jr. 126, 152 ; C. -M- 

327; M. 227, 291, 314 
Halley {portr.) 50, 105,. 

107, 181, 182, 184, i86-8 y 



Index 



415 



197, iQ9, 204, 208, 269, 

Hamburg, 277 

Hamy 390 

Hansen 26, {portr.) opp. 
20, 27, 103, 3S9 

Harding 155, 397 

Harkness 25, 51, 53, 54, 
S7, 101, 148,206,390,393 

Harmonia (^o) 39S 

Harrington 240, 390 

Harrison, H. 33 ; J. 
{Portr.) 372, 373. 

Hartleben vii 

Hartwig 148, 178 

Harvard Coll. Obs. 238, 
258? 3oo> 330 

Harvey 230 

Harzer 148 

Hasselberg 204 

Hastings 88, 332, 35 6_ 7> 
386-7 

Haughton 80 

Hebe (6) 397 

Hecate (100) 399 

Hecuba (108) 399 

Hedda (207) 402 

Heidelberger (325) 405 

Heis 227-9, 241, {portr.) 
256 

Helena (101) 399 

Heliometer 55, 277, 390 

Helium 78 

v. Helmholtz {portr.) 77, 
247* 253 

Hencke 397 

Henderson 274 

Henrietta (225) 402 

Henry Bros, vi, opp. 28, 
128, 138, 154, 237, 331, 
341,347-393, 400-1 

Hera (103) 399 

Hermentaria (346) 405 

Hermione (121) 400 

Herschel, A. S. 222, 229; 
C. {portr.) 189, 190 : J. 
14*74,76,80,99, 128,154, 
156, 184, 191, 206, 245, 
251, 269, {portr.) 302, 
303-5, 307-10, 322,386; 
W. ii, 1,2, 8, 13, {portr.) 
14, 80, no, 128-9, J37-8, 
155, 160, 245, 253, 279- 
8i, 288, 303-4, 322-23, 
325, 384, 388 

Hersilia (206) 402 

Hertha (135) 400 

Herz 33:39° 

Hesperia (69) 398 

Hestia (46) 398 

Hevelius 155, 266, 269, 
318-9,365-6 

Heyde339, 355> 357 



Higgins 240 

Higgs 72-3, Si 

Hilda (153) 400 

Hill, G. W. 27, 103, 151 ; 

R. 24! 
Himmel tind Erde vi 
Hind 103, 186-7, 198,206, 

266, 397 
Hipparchus 9, 255 
Hirn 152, 207, 254 
Hoek 206 
Holcomb 324-5 
Holden 178, 311, 395 
Holetschek 207 
Hollis 387 
Holmes 196-7 
Honoria (236) 403 
Hooke 155 
Horrox 107 
Hough 118, 120-1, 151, 

39o 
Houghton, Mifflin & Co. 

vii 
Houzeau 18, 33, 80, 147, 

191, 206-7, 241, 394 
Hubbard 192 
Huberta (260) 403 
Huggins, Lady 154, 305, 

390; Sir W. 16, 79, 80, 

88, 119, 128, 140, 154, 

174, 179, 204, 206, 246, 

289, 294, 305, 310-12, 

3i4 
v. Humboldt 209 
Hungaria (434) 407 
Huntington 230 
Hunyadi 187 
Hutchins 72 
Huxley 25 
Huygens T2, 129, 131, 155, 

180, 307 {portr.) 317, 

318-9 
Hygeia (10) 397 
Hyginus 292 
Hypatia (238) 403 
Hyperion 129, 131 

Ianthe (98) 399 
Idea (286) 404 
Ida (243) 403 
Ideler 40, 240 
Idunna (176) 401 
Ilmatar (385) 406 
Use (249) 403 
Ingeborg (391) 406 
Ino (173) 401 
Invariable plane 98 
Io 121^(85)399 
Iphigenia (112) 399 
Irene (14) 397 
Ins (7) 397 
Irma (177) 401 
Isabella (210) 402 



Isis (42) 398 
Ismene (190) 401 
Isolda (211) 402 
Istria (183) 401 

Jablonow 18 

Jacoby 392 

Jahn 18 

James, A. C- 362 ; D. W. 

360 ; Mrs D. W. iii 
Janssen 16, 60, 62, 68, 73, 

85, 128, 178, 180, 201,. 

254,313,392, 395 
Japetus 129 
Javelle 163, 193 
Jeans 241 
Jewish Era 40 
Johanna (127) 400 
Johns Hopkins Univ. vi,. 

356 
Johnson, A. J. 387, 392; 

S. J. 88 
Johnston 241 

Jones, G. 227-8 ; G. S. 388 
Josephina (303) 404 
Josephus 186 
Joule 229 
Jour. Brit. A sir. Assoc, 

89, 3*5 
Juewa (139) 400 
Julia (89) 399 
Juno (3) 397 
Jupiter 1 16-126 
Justitia (269) 403 

Kaiser 103, 148, 156,. 

{portr.) 157, 390 
Kant {portr.) 245, 253 
Kapteyn 260, 295, 306,. 

313-14, 348-9, 394 
Karl 389 

Katharina (320) 405 
Kayser 73 
Keeler 79, 81, 112, 118— 

20, 122, 128, 134, 140, 

151, i53, i54, i75, i79, 

254, 310, 313,387, 389 
Kelvin, Lord 23, 25, 77, 

80, 81, 248 
Kempf 151, 313 
Kepler 10, 48, (portr.) 92, 

93, 181, 188, 253, 266 
Kepler's Laws 92 
Keyser 231 
King 25 
Kirchhoff 16, 70, {portr. )) 

■j 1, 72, 80, 85, 246 
Kirkwood 103, 114, 115,. 

134, 149, 206, 207, 229^ 

230, 253 
Kleiber 198 
Klein 103, 24r, 254 
Klumpke, Mile 260 



414 



Index 



Knight, E.H. 386; W.H. 

386 
Knobel, 156, 159-60, 162, 

*79, 3ii 
Knopf, 81 
Knorre 401-3 
Knowledges'^ 89,207, 315 
Kobold 89 
Kolga (191) 401 
v. Konkoly 63 ,229, 390, 393 
Kreutz 200 
Krieger 33 
Kriemhild (242) 403 

Lacadiera (336) 405 
Lacaille 231, 233, 270, 

287, 308 
Lachesis (120) 400 
Lacrimosa (208) 402 
Laetitia (39) 398 
La Fouge 254 
La Grange 12, 96, {portr.) 

■r 97 . 

La Hire 195 

Lalande 18, opp. 18, 145, 

274 
Lambert 253 
Lamberta (187) 401 
Lameia (248) 403 
Lamey 151 
Lamont {portr.) 308 
Lancaster 33, 80, 147,391 
Landerer 151 
Lane 77, 247, 248 
Langley vi, 33, 68, 70, 

74-6, 80-1, 85, 207, 390, 
r 395 
La Place 12, 18, 96-7, 123, 

135. 245, {portr.) 246, 

248-9, 252-4, 374 
Lassell 123, 128, 132, 138, 

i4S> l 5 6 , 322, 388 
Latitude variation 3, 23 
Laurent 398 
Laurentia (162) 401 
Le Chatelier 77, 8i 
Leda (38) 398 
Ledger 103, 147 
Legion of Honor opp. 18 
Lehmann-Filhes 229 
Lemstrom 25 
Leon a (319) 405 
Leonard, Miss opp. 108 
Leonids 209-14, 360 
Lescarbault 147 
Lesser 398 
Leto (68) 398 
Leucothea (35) 397 
Le Verrier opp. 26, 53, 96- 

7, 100, 103, {portr.) 142, 

143-4 » 146-8, 150, 152-4 
lewis, G. C. 18; H. C. 

229 ; T. 40, 387, 394 



Lexell 137, 196, 197 
Liais 149, 154, 227 
Liberatrix (125) 400 
Libussa (264) 403 
Lick 125, {portr.) 380 
Lick Obs. 335, 379, 395 
Lick telescope 288 
Light 3 

relations of 41 
velocity 43 
Ligondes 254 
Lilaea (213) 402 
Linsser 160 
Lippmann 391 
Littrovv 332 
Liverpool Astr. Soc. opp. 

86 
Lockyer, Sir N. 16, 18, 69, 

72, 80-1, 89, 154, 156, 

J 79> 230, 254, 301, 312 
T -14,389,390; W.J. 179 
Loschardt 149 
Loewy vi, opp. 30, 33, 141, 

340, 39°> 394 
Lohrmann 31, 33 
Lohse, J. G. 206; O. 116, 

150, 156, 178-9 
Lomia (117) 400 
Longmans, Green & Co. 

vii 
Loomis 18, 154, {portr.) 

383, 391,396 
Loreley (165) 401 
Louis xiv. 141 
Love 391 
Lovering 25 
Lowell vii, opp. 108, 123, 

x 48-9, i57> i59, l6l > 
opp. 162, 163-4, 167-8, 
170-71, 175, opp. 176-7, 
17.9, 336, 354, 379 

Lucia (222) 402 

Lucina (146) 400 

Lucretia (281) 404 

Ludovica (292) 404 

Lumen (141) 400 

Lundin 336 

Lutetia (21) 397 

Luther 397-400, 403-4 

Lydia (no) 399 

Lyman, A. J. 325 ; C. S. 
in, 148; J. 325 

Lynn {portr.) v, 89, 207, 
392 

McClean vii, opp. 72, 73, 

81,314 
McClure 241 
McLeod 68 
Macrinus 186 
Masdler 26, 31, 103, no, 

*«i i37i 155* i64-5) 

291, 3 X 3 



Magdalena (318) 405 
Magelhaens 302 
Magnetic decl. 67 
Mahler 40 
Mahometan Era 40 
Maia (66) 398 
Main 18, 391 
Manila 88, 392 
ManoraObs. 377 
Mantois 328 
Margarita (310) 404 
Maria (170) 401 
Mars in 

atmosphere 173-6 

axis 159 

canals 165-8 

changes 156 

charts opp. 176-7 

climate 175 

doubling of canals, 
170 

drawings 156 

favorable oppositions 
159, 160, 177 

first obs. 155 

lakes 163 

maps 155 

motion 92 

oases 163 

1 Oculus ' 164 

orbit 408 

parallax 51 

photography 156 

polar caps 155, 159 

projections 162 

seas 158 

sketches 156 

terminator 162 

topography 158 

water on 158, 177 
Marth 118, 397 
Martha (205) 402 
Martin 324 

Mascart, E. 80; J. 149 
Maskelyne, N. 273, 288; 

N. S. 229 
Mason 325, 388, 396 
Massalia (20) 397 
Matilda (253) 403 
Matson 180, 254 
Maunder 16, 63, 68, 81, 
151, i74, 178-9, 289, 314 
-15, 387, 389; Mrs 87, 89 
Maury 312 
Maximiliana (65) 398 
Maxwell 42, 94, 136, 152 
May (348) 405 
Mayer, A. M. 120; J. R. 

253 ; T. {portr.) 373 
Mayr 121, 308 
Measuring engine 348 
Mecanique Celeste 12, 97 
Mechain opp. 18, 189, 194 



Index 



415 



Medea (212) 402 
Medusa (149) 400 
Mee 396 
Meisel 178 
Melbourne 259 
Melete (56) 39S 
Meliboea (137) 400 
Melpomene (18) 397 
Menippe (iSS) 401 
Mercury 104-7 
Meridian Circle 365, 367 

-S 
Merriam Co. vii 
Merz & Mahler 330 
Messer 241 
Messier 196, 251, 310 
Meteors 9S, 20S, 220 

Andromedes 219 

August 215 

bibliography 22S-30 

connection with com- 
ets 209 

fireballs 214 

Leonids 209-14 

November 209-14 

orbits 213 

origin 217 

Perseids 215 

photography 212, 358 

-9 

radiant 209, 211, 216 

showers 216 

telescopic 214 
Meteorites 213, 220 

bibliography 22S-30 

classification 224 

collections 221 

composition 227 

fall at Orne 222 

flight 222 

form 223 

iron 225 

metallic 224 

Ovifak 226 

stony 224 

temperature 222 

velocity 222 

Widmanstattian figs. 
225 

worship of 221 
Metis (9) 397 
Meton 37 
Metonic Cycle 37 
Meunier 178-9, 229 
Meyer, H. J. 68, 392 ; 
If. W. 152, 179, 201, 
206, 392 
Michell 280 
Michelson 44, 389-90 
Micrometers 342-3 
Miers 230 
Mill 25 
Miller, W. 180; W. A. 16 



Millosevich 404 
Mimas 129 
Minerva (93) 399 
Miriam (102) 399 
Mirror, silvering 324 
Mitchel 241, {portr.) 330 
Mitchell 33, 203, {portr.) 

204 
Mnemosyne (57) 398 
Monachia (42$) 407 
Monck 115, 230, 314 
Montaigne 192 
Mont Bianc 395 
Month 36 
Montigny 311 
Montucla 18 
Moon 26 

bibliography of 33 

craters 3 1 

distance 28 

motion 26 

perturbations 26 

photographs of 28-31 

rills 32 

size 30 

streaks 32 

surface 30 

tables of 27 
Motion, laws of n 
Mouchez 347, 393 
Mouchot 76 
Moulton 254, 313 
Mountain observatories 

395 . 
Mountings 339 
Miiller 14S, 175, 207, 311, 

313-14,391 
Myers 314 

X AEG AM VELA 364 

Napoleon 188 
Xarrien 18 
Nasini 79 
Nasmyth 33 
National Museum 224 
Mature vi 
Nausicaa (192) 401 
Navigation 1, 26, 372-4 
Nebulas 299-310 

Andromeda 243 

Argus 265, 350 

Canes Veil. 310 

distribution 304 

Lyra 309 

Orion 23S 

photographs 23 8, 243, 
265, 309, 310,350 

spectra 3 10 

spiral 309-310 

variability 309 

Virgo 251 
Nebular hypothesis 245 
Neison 33 



Nemausa (51) 398 

Nemesis (12S) 400 

Nenetta (289) 404 

Nephthys (2S7) 404 

Neptune 140-7 

Nevill 26 

Newcomb viii, 23-5, 27, 
44, 53, 55, 63, 77, 85, 
88, 100, 105, 109, 116, 
129, 139, 146-9, 152-4, 
241, 253, 311-12, 346, 
386-7,389, 390-3... 

Newton, H. A. viii, 206 
-7, 209, 211-12, {portr.) 
opp. 212, 217, 224, 229- 
30 ; Sir I. 11-12, 16, 
{portr.) 93-4, 154, 181, 
186, 320-1, 326 

Newton's Law 11, 12, 93 

Nice Obs. 169 

Nicholas 1. 130 

Niesten 107, no, 115, 148 
,79, *5 6 , *58, i79 

Nike (307) 404 

Niobe (71) 398 

Noble 396 

Nolan 254 

Nordenskiold 226 

Norton 185, 206 

Nutation 23 

Nuwa (150) 400 

Nyren 23, 47, 253 

Nysa (44) 39S 

Oberon 138 

Object-glass, achromatic 
. 32 7,332,35 6 ; bibliogra- 
phy 387; cost 336; 

mount 336; photogra- 
phic 331, 351 ; triple 

331 ; weight 337 
Obrecht 53 
Observatories 316, 374, 

391, 395 ; construction 

375-7 ; first Am. 329 ' r 

mountain 379-83, 395; 

sites 374, 37S-80 
Observatory {illustrated) 

Boyden 264, 382 

Capetown 277 

Dantzig 366 

Greenwich 39 

Harvard 300 

Lick 122 

Lord Rosse 247 

Manora 377 

Nice 169 

North field 368 

Oxford 376 

Paris 141 

Potsdam 61 

Pulkowa 130, 133; 

Roberts 290, 292 



4i6 



Index 



Observatory (illustrated} 
Smith College 375 
Vienna 334 
Washington 101 
Yerkes 337 

'Observatory ', The vi, 89, 
207, 396 

Oceana (224) 402 

CEnone (215) 402 

Olbers 114, (portr.) 153, 
189, 197, 207, 397 

Olga (304) 404 

Oliver 396 

•Olmsted 209, (portr*) 210, 
228, 329 

Olympia (59) 398 

Opelt 33 

Ophelia (171) 401 

Oppavia (255) 403 

Oppolzer, E. 68; T. 
(portr.) opp. 86, 89, 206 

Opticians 331 

Orbit, comet 181-2 ; 
Earth's 22 ; elements 
96 ; planets' 99 ; secu- 
lar variations 97 

Orion nebula 238 

Ornamenta (350) 405 

Ostara (343) 4°5 

Ottilia (401) 407 

Oudemans 152 

Ovid 292 

Ovifak, Greenland 226 

Oxford Obs. 376 

Paine 381 
Pales (49) 398 
Palisa 86, 400-5 
Palitzsch 182 
Pallas 222 
Pallas (2) 114, 397 
Palmer 203 
Pandora (55) 398 
Pannekoek 314 
Panopa^a (70) 398 
Pariana (347) 405 
Paris Obs. opp. 26, 100, 

141, 237 
Parkes 254 
Parkhurst 115, 149 
Parsonstovvn 247 
Parthenope (11) 397 
Paulg 

Paulina (278) 404 
Payne vii, 207, 367, 392 
Peal 179 
Pearson 396 
Peck 241 
Peirce 80, 135, {portr.) 

136, 146, 152, 206, 253 
Peitho (ir8) 400 
Pendlebury 387 
Penelope (201) 402 



Penthesilea (271) 403 

Perihelion 54 

Perrotin no, 139, 148, 

I 5 2 , 154, 162, 169-70, 

178-9* 39i> 400-1. 403. 
Perry 68 (portr.) opp. 

86 
Perseids 215 
Perseus cluster 297 
Personal equation 370, 

39o 
Peters, C. A. F. 23, 

(portr.) 274, 275; 

C. F. W. 207, 396; 

C.~H. F. (portr.) 113, 

i47» 241, 33i> 39 8 -404 

Peurbach 10 

Phaedra (174) 401 

Phaso (322) 405 

Phaethusa (296) 404 

Philagoria (274) 403 

Philia (280) 404 

Phillips 240 

Philomela (196) 402 

Philosophia (227) 402 

Phipson 229 

Phobos 112 

Phocaea (25) 397 

Phocylides 269 

Photo-chronograph 371, 
39o 

Photography 3 ; advances 
365 : bibliography 393 
-5 ; lunar 30 ; nebular 
238, 243, 265, 309-10; 
planetary 115, 119, 128, 
156; solar 57-65; stel- 
lar 237, 257-65, 271, 
279, 285-301 

Photo-heliograph 345, 393 

Photo-tachometer 44 

Phthia (189) 401 

Phythian vi, 101 

Piazzi 397 

Picard 12, 317, 365 

Piccolomini 231 

Pickering, E. C. vi, viii, 
16, 70, 128, 131, 139, 
145-6, 152, 258-9, 263, 
286, 295, 298, 306, 311 
-i2> 349, 35 1 , 360, 386, 
39o, 393-5 > 4o8; W. H. 
32-3, 86, 107, 123-4, 
i5 r > 156-7, i59, i°i> 
163-4, 167, 172-3, 178-9, 
230, 309, 394 

Pierretta (312) 404 

Pigott 197 

Planets 94, 104 

bibliography 147-54 
distances 98 
elements 96, 102 
inferior 104 



Planets (continued) 

intramercurian 100, 

14.7 
Jupiter 116-26, 150 
Mars in, 147, 155 
mass 90 

Mercury 104-7, J 48 
Neptune 140-7, 154 
orbit 99, 104 
photography 115, 119, 

128 
relative size 95 
Saturn 122-36, 151 
small 15, 102, 113, 

i49., 355,397-4o8 
superior 104 
tables of 100, 140 
trans-Neptunian 103 
Uranus 136-40, 153 
Venus 104-10, 148 

Plassmann 230 

Pleiades 236-7 

Plummer 207, 311, 386 

Poggendorff* 386 

Pogson 398-9, 403 

Poincare 103, 152, 250-2 

Poisson 96 

Polana (142) 400 

Pole wanderings opp. 24 

Polyhymnia (33) 397 

Polyxo (308) 404 

Pomona (32) 397 

Pompeia (203) 402 

Pons 183, 1S8-9, 192, 197 

Pontecoulant 26, 182 

Poole 25, 33, 81, 88, 180, 
207, 230, 254, 315, 395 

Poona Obs. 65 

Poor 197, 389 

Popular Astronomy vi, 
89, 207, 367, 396 

Porter 180, 312 

Potsdam 60-1 

Pottier 151 

Pouillet 76 

Preston 25 

Prevost 288 

Princeton Univ. vi, viii 

Principia 12 

Prinz 31, 33 

Pritchard 258, 279,312,393 

Pritchett 153 

Procne (194) 401 

Proctor vii, 33, 59, 67, 89, 
121, 148, 152, 156, 180, 
206, 232, 241, 253, 
(portr.) 305, 311-12, 
392, 39 6 

Prominences 59-67 

Proserpina (26) 397 

Protogeneia (147) 400 

Protuberances 59-67 

Prymno (261) 403 



Index 



417 



Psyche (16) 397 
Ptolemy 10. 1x6, 244 
Puiseux, P. opp. 30, 33, 

V. 53 
Pulkowa 12,3,0pp. 212, 335 

Radau 313, 390 
Rambaut 312 
Rammelsberg 226, 229 
Ramsay 7S, 81, 230 
Rankine 253 

Ranyard 88, 128, 202, 279, 
{portr.) 326, 3S6, 392, 

395 
Rayet 295, 311, 391, 393 
Reed 389 

Reflector {see Telescope) 
Reflector, silvering 388 
Refraction 41 
Refractor {see Telescope) 
Regina (285) 404 
Regiomontanus 10 
Repsold 277, 337, 339, 348 
Resisting medium 95, 191 
Reversing layer 78, 87, 

364-5 
Rhea 129 
Rhodope (166) 401 
Riccioli 155 
Ricco 63, 65-6 
Ritchie 178 

Rittenhouse {portr.) 329 
Roberta (335) 405 
R.oberts vi, 23S, 243, 290, 

292-3, 297, 309-10, 313, 

3i5i 323, 367, 375. 394 
Roche 136, 253 
Romer43, {portr.) 45, 46, 

3^7, 365 
Rogers, J. A. 390 ; W. A. 

315 

Rohrbach 241 

Rosa (223) 402 

Rosalia (314) 404 

Rose 224, 229 

Rosette & Feil 32S 

Rosse 8, 33, 150, 156, 245, 
247, {portr.) 248, 309, 
311, 322, 325, 384, 388 

Rossetti 77 

Roszel 114, 149 

Rothman 18 

Rowland vi, 71-3, 76, 81 

Roxana (317 

Riimker 203 

Ruling engine 72 

Runge 73 

Russell 309-10, 312-13, 

Russia (232) 402 
Rutherfurd 30, 52, 57, ~i, 

76, 174, 279, {portr.) 

344, 387. 393 



Sadler 241 

Saegmuller 339, 342, 369 

Safarik 148 

S afford 398 

St Augustine ii 

Salmoiraghi 339 

Sampson 68 

Samter 313 

San ford 390 

Sapientia (275) 403 

Sappho (80) 399 

Saros 84 

Satellites 26, 91, 109, 112, 

121, 12S, 138, 145 
Saturn 122-136 
Sawitsch 396 
Schaeberle 124, 151, 164, 

179, 202, 325, 346, 388, 
394 

Scheiner vii, 76-7, 81, 103, 
120, 178, 205, 207, 301, 
312-14, 389, 394 

Schiaparelli 105-7, opp. 
108, no, 137, 139, 148 
-49, i53i 156-9, 162, 
164-8, 170, 174, 178-9, 
215, 229-30, 283, 314, 
393 

Schmidt, A. 79, 8r ; J. 
F- J. 31, 33, n8, 227-8, 
267 ; R. 149 

Schonfeld 241, {portr.) 
270, 272 

Schooling 393 

Schorr 148 

Schram 40 

Schroeder 331 

Schroeter no, 148, 17S 

Schubert 96 

Schulhof 195, 230, 400 

Schumacher 103 

Schur 151, 175 

Schurig 241 

Schuster 79, 85-6, 202, 
389 

Schwabe 57, 60 

Schwann vi 

Schwassmann 407-8 

v. Schweiger-Lerchenfeld 
vii, 33, 3M, 394 

Scylla (155) 400 

Searle, A. 229 ; G. M. 

180, 39S 

Secchi vii, 16, 58, 67, 77, 
123, 128, 156, 174, 183, 
{portr.) 294, 295, 311 
Secretan 339, 369 
Secular variations 97 
See v. 249-52, 254, 284, 

313,395 
Seehger 103, 152, 390 
Selenography 26 
Semele (86) 399 



Seneca 202 
Serpieri 227, 229 
Serviss 180, 241, 396 
Servus 386 
Sestini 67 
Sextants 390 
Shackleton 87 
Shadow, lunar 83 
Shadwell 389 
Shepard 221, 223 
Sibylla (168) 401 
S icier ens Nuncius 120 
Sidgreaves 63 
Siemens 80 
Signs of zodiac 234 
Silesia (257) 403 
Siri (332) 405 
Sirius, spectrum 294 
Sirona (116) 400 
Sita (244) 403 
Siwa (140) 400 
Smith, H. J. S. 180; 
H.L. 325, 387-8; J.L. 
213, 221, 226, 228 
Smith Coll. Obs. 375 
Smithsonian Inst, vi 
Smyth, C. P. 72-3, 80, 
227, 395; W. H. 311, 
396 
Snell 42 
Solar system 90 

bibliography 103 

bodies of 91 

stability 96 
Somerville {portr.) 150 
Sophia (251) 403 
Sophrosyne (134) 400 
Souch.on 396 
Souillart 151 
Spectroheliograph 63, 352, 

389 
Spectroscope 353, 389, 

395 ; testing obj. 387 
Spectroscopy 389 
Spectrum, infra-red 74 

normal 74 

solar opp. 72 

stellar 295 

ultra-violet 75 
Spectrum analysis 15, 16 

principles of 70 
Spencer, C. A. 330 ; H. 2 54 
Spitaler 207 
Spoerer 57, 65-8, 77, 

80 
Stanford vii 
Stanley 254 
Stars, Algol 270 

Argus 17 265, 269, 350 

astrogr. survey 260 

binary 250-1, 2S1-5 

bright line 295 

brightness 258 



4i8 



Index 



Stars {continued) 

Carinas, Eta 265, 350 
catalogues 9, 255-6 
Centauri a 250, 275, 

278 ; oi 269 
central sun 291 
charting 260, 347 
clusters 269, 291, 293, 

2971 3?4 
composition 294-301 
Cygni 61, 274 
distances 15, 272-280 
distribution 303-6 
double 251, 276-83 
Durchmusterung 261, 

305 
fixed 255 
Galaxy 257, 295 
gauges 303 
Gesellschaft zones 

261 
lucid 256 
magnitudes 256 
Milky Way 257, 295 
motion in sight line 

289 
nearest 274 
new 255-69 
Nova Aurigae 267 
Nova Cygni 267 
orbits 250, 284 
parallaxes 272-280 
photography 237, 257, 

260,263-5,271,279, 

285-7, 289-94, 297 

-301, 350 
photometer 258 
proper motions 284-9 
Sirian 295, 306 
solar 295, 306 
solar motion 287 
spectra 294-302, 350 

"5 1 
spectroscopic binaries 

284-7 
temporary 255-69 
Ura?iom. Arg. 262 
variables 271 
Staus 405 
Steinheil 331 
Stephan 399 
Stephania (220) 402 
Stockwell 96, 98, 103 
Stokes 354 
Stone, E. J. 51, 53, 149; 

O. 309 
Stoney 149, 176, 179, 388, 

39°, 392 
Stonyhurst Obs. opp. 86 
Strassmayer 18 
Stroobant 109, 152 
Struve, H. 129, 136, 152, 
154; L.33; O.129, 132, 



(portr.) 133, 278, 283, 
393 ; W. 182, 190, 281, 
{portr.) 282, 283, 311, 
328, 391 
Stuyvaert 107, no 
Sun ii, 4, 48, 69 

bibliography of 67-8, 
80-1 

chromosphere 65, 78 

composition 72 

constitution 78 

density 54 

diameter 54, 55 

distance 48-54, 107, 
408 

faculae 56, 58, 64 

form 55 

gravity 55 

heat 76 

light 70 

maintenance 77 

mass 54, 90 

parallax 4S-54 

photography 57-65 

photosphere 78 

power of 69 

prominences 59-67, 78 

radiation 76 

reversing layer 78, 87, 

364-5 
rotation 56 
shrinkage 77 ^ 
spot periodicity 57 
spots 52, 56-62, 66-7 
spot-zones, law of 66 
temperature 77 
theory of 79 
volume 54 

Surveying 1 

Svea (329) 405 

Svedstrup 149 

Swedenborg 253 

Swift, E. 195 ; L. 147, 
188, 194, 197, 217, 308, 
386, 391 

Sydney 259 

Sylvia (87) 399 

Symons 25 

Tacchini 63, 67 

Tacubaya 259 

Tait 80, 94, 206 

Tamara (326) 405 

Tannery 18 

Taylor, A. 140, 154; 

H. D. 331, 387, 394; 

W. B. 94 
Taylor & Francis vii 
Tebbutt 184, 201, 204 
Telescopes 2, 6-8, 316, 

386, ^88, 395 
ac iromatic 327 
aerial 319 



Telescopes {contimied) 
American 324 
ancient 318 
coude 340, 388, 390 
future 7, 8, 384-6 
great 322, 333-8, 384, 

.386-7 
history 386 
literature 386-96 
mounting 386, 388 
objectives 387 
photographic 331, 344 
portable 377 
reflecting 320, 3S8 
refracting 3241!. 386 
testing 387 

Telescopes {illustrated) 
almucantar 371 
astrographic equa- 
torial 259 
Bache 299 
Bruce telescope 264 
coude equatorial 340 
eclipse instruments. 

361-2 
field-glass 319 
heliometer (Cape- 
town) 277 
HerschePs 40-ft. 13 
Hevelius 318 
Lick 36-in. 124, 125 
Lord Rosse's 247 
Melbourne 4-ft. 322 
meridian circle 368 
merid. photometer250- 
photographic equa- 
torial 357 
photo-heliograph 345 
portable 377 
Potsdam equatorial 60 
Pulkowa 30-in. 133 
reflector (Brashear) 

321 
Roberts 292 
spectro-heliograph 

352 
Vienna 27-in. 333 
Yale (meteor photo- 
graphy) 212 
Yerkes 40-in. 338 

Tempel 115, 194, 197, 204, 
217, 398-99 

TenerifFe 395 

Terao 354 

Terby 128, 148, 156, 162, 
170, 178-79 

Tercidina (345) 405 

Terpsichore (81) 399 

Tethys 129 

Tewfik 202 

Thalen 72 

Thalia (23) 397 

Themis (24) 397 



Index 



419 



Theodori 231 
Theodonc 1S6 
Theodosius 259 
Theresia (295) 404 
Thetis (17) 3-J7 
Thisbe {$$) 399 
Thollon 72-3, Si, 139* 206 
Thomson 253 
Thora (299) 404 
Thornthwaite 388 
Thule (279) 114, 404 
Thulis 189 
Thusnelda (219) 402 
Thyra (115) 399 
Tides 248 
Tietjen 399 
Time, equation of 21 
Timour 10 
Tirza (267) 403 
Tisserand 115, 125, 136, 

(portr.) 146, 147, 149, 

.151-52, 154, i79> 207 
Titan 129, 131 
Titania 138 
Titus 186 
Todd, D. P. 53, 103, 148 

-50, 265, 280, 345, 361 

-63, 386,390, 391, 3^5; 

M r s vii, 89 
Todhunter 25 
Tolosa (138) 400 
Transits, Mercury 105 ; 

Venus 50, 53, 107-9 
Tromholt 25 
Trouvelot 63, 86, 108, 128, 

148-9, 151-52, 156, 178 
Trowbridge, D. 253 ; J. 

72, 80 
Tschermak 229 
Tuckerman, A. 68, 254, 

389 
Turner 376, 390, 394 
Tuttle 193-94. i97> 398 
Twining 209 
Tyche (258) 403 
Tycho vii, 10, ( portr.) 91, 

92, 199, 263, 317 
Tychonic System 10 

Ulugh Begh 10 
Umbriel 138 
Una (160) 401 
Undina (92) 399 
Undulatory theory 42 
Unitas (306) 404 
Unterweger 68, 206 
Updegraff"39i 
Upton 241, 391 



Urania (30) 397 
Uranus opp. 18, 136-40 
Urda (167) 401 

Vade Mecum 18, 33, 207, 
394 

Vala (131) 400 

Valda (262) 403 

Valentiner 33, 40, 89, 254, 
313, .387, 392 

Vanadis (240) 403 

Van der Willigen 80 

Vaticana (416) 407 

Velleda (126) 400 

Venus 104-10 

Vera (245) 403 

Vernal equinox 22, 234 

Very 33, 68 

Vesta (4) 114, 397 

Vibilia (144) 400 

Victoria ( \2) 397 

Viertelj ahrsschrift A G. 
vi, 392 

Villars vii 

Villiger 148, 407-8 

Vindobona (231) 402 

Virginia (50) 398 

Vogel 16, 61, 70, 72, 76, 80, 
81, 119, 128, 140, 148, 
149, 174, 204, 289, 295, 
301, 3*1-13.386,388 

Wadsworth 80, 326, 388 

-9. 392, 394 
Walker 146 
Wallace 25 
Walpurga (256) 403 
Warner & Swasey vi, 339, 

34?,. 369. 386 
Washington Obsy 100, 

101, 375 
Waters 304 
Watson 147, (portr.) 152, 

206, 399-401 
Watts 80 
Waugh 151 
Webb 33, {portr.) 378 

396 
Weinek 31, 33 
Weiss 2o\ 241, 334 
Wendell 230 
Weringia (226) 402 
Wesley 89 
West 240 
Wetstein 95 
Whewell 180 
Whitall 240 
White 186 



Whitney 314 

v. Widmannstatten 226 

Wilczynski 68 

Wilhelniina (392) 406 

Williams, A. S. 118-20, 
126, 151, 153, 163, 165, 
168, 170-71, 173, 178 
-79; G. 183 ; M 175 

Wilson, H. C. 120, 162 
168, 178-79, 206-7, 230, 
314; J.M. 311; W. E. 
77< 81 

Winlock, J. 345 ; W. C. 
206 

Winnecke 193, 197, 202, 
204, (portr.) opp. 212 

Winterhalter 391, 393 

Wislicenus 40, 156, 178 

Witt 153, 392, 407 

Wolf, C. 253, 295, 311 ; 
M. 15, 190, 195, 197, 
212, 355, 405-8; R. 18, 
57, 147, 386 

Wolfer 67, 68 

Wollaston 16 

Woods 347 

Woodward 25 

Wright 206, 227-8, 230 

Wulfing 230 

Wurdemann 32 

Xantippe (156) 401 

Vale Obsy. 329, 383; 

Univ. viii. , 209, opp. 212, 

224 
Yarnall 312 

Year, sid. and tropical 22 
Yendell 314 
Yerkes Obsy. 324, 335, 

337 
Young, C. A. vi,' viii, 16, 
18,51,56,62-3,67-8, 70, 
72,77-8,81,85, 137, 139, 
154, 178-9, 19^, 204, 
206, 241, 3'5> 335, 386 

-7, 389-91 > J- 44 

Yrsa (35 4°5 

v. Zach (portr.) 370, 371 
Zahrineia (421) 407 
Zeitschriftfiir Inst. 391 
Zelia (169) 401 
Zeneer 149 
Zodiac 234 
Zodiacal light 227 
Zollner 68, 77, 206 
Zucchi 1 16 



APR 17 1899 



